Systems and methods for multi-color led pixel unit with horizontal light emission

ABSTRACT

A micro multi-color LED device includes two or more LED structures for emitting a range of colors. The two or more LED structures are vertically stacked to combine light from the two more LED structures. Light from the micro multi-color LED device is emitted horizontally from each of the LED structures and reflected upward via some reflective structures. In some embodiments, each LED structure is connected to a pixel driver and/or a common electrode. The LED structures are bonded together through bonding layers. In some embodiments, planarization layers enclose each of the LED structures or the micro multi-color LED device. In some embodiments, one or more of reflective layers, refractive layers, micro-lenses, spacers, and reflective cup structures are implemented in the device to improve the LED emission efficiency. A display panel comprising an array of the micro tri-color LED devices has a high resolution and a high illumination brightness.

RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 63/034,394, filed Jun. 3, 2020, entitled “SYSTEMS AND METHODS FORMULTI-COLOR LED PIXEL UNIT WITH HORIZONTAL LIGHT EMISSION,” which ishereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates generally to light-emitting diode (LED)display devices, and more particularly, to systems and fabricatingmethods for LED semiconductor devices that emit different colors withhigh brightness and micro-meter scale pixel size.

BACKGROUND

With the development of Mini LED and Micro LED technology in recentyears, consumer devices and applications such as augmented reality (AR),Virtual Reality (VR), projection, heads-up display (HUD), mobile devicedisplays, wearable device displays, and automotive displays, require LEDpanels with improved resolution and brightness. For example, an ARdisplay integrated within a goggle and positioned close to a wearer'seyes can have a dimension of a fingernail while still demanding an HDdefinition (1280×720 pixels) or higher. Many electronic devices requirecertain pixel size, distance between adjacent pixels, brightness, andviewing angle for the LED panels. Often, when trying to achieve themaximum resolution and brightness on a small display, it is challengingto maintain both the resolution and brightness requirements. Incontrast, in some cases, pixel size and brightness are difficult tobalance at the same time as they can have an approximately oppositerelationship. For example, getting a high brightness for each pixelcould result in a low resolution. Alternatively, obtaining a highresolution could bring the brightness down.

Generally, at least red, green and blue colors are superimposed toreproduce a broad array of colors. In some instances, to include atleast red, green and blue colors within a pixel area, separatemonochromatic LEDs are fabricated at different non-overlapping zoneswithin the pixel area. The existing technology faces challenges toimprove the effective illumination area within each pixel when thedistance between the adjacent LEDs is determined. On the other hand,when a single LED illumination area is determined, further improving theoverall resolution of the LED panel can be a difficult task because LEDswith different colors have to occupy their designated zones within thesingle pixel.

Active matrix liquid-crystal displays (LCD) and organic light emittingdiode (OLED) displays combined with thin-film transistor (TFT)technology are becoming increasingly popular in today's commercialelectronic devices. These displays are widely used in laptop personalcomputers, smartphones and personal digital assistants. Millions ofpixels together create an image on a display. The TFTs act as switchesto individually turn each pixel on and off, rendering the pixel light ordark, which allows for convenient and efficient control of each pixeland of the entire display.

However, conventional LCD displays suffer from low light efficiency,causing high power consumption and limited battery operation time. Whileactive-matrix organic light-emitting diode (AMOLED) display panelsgenerally consume less power than LCD panels, an AMOLED display panelcan still be the dominant power consumer in battery-operated devices. Toextend battery life, it is desirable to reduce the power consumption ofthe display panel.

Conventional inorganic semiconductor light emitting diodes (LED) havedemonstrated superior light efficiency, which makes active matrix LEDdisplays more desirable for battery operated electronics. Arrays ofdriver circuitry and lighting-emitting diodes (LEDs) are used to controlmillions of pixels, rendering images on the display. Both single-colordisplay panels and full-color display panels can be manufacturedaccording to a variety of fabrication methods.

However, the integration of thousands or even millions of micro LEDswith pixel driver circuit array is quite challenging. Variousfabrication methods have been proposed. In one approach, controlcircuitry is fabricated on one substrate and LEDs are fabricated on aseparate substrate. The LEDs are transferred to an intermediatesubstrate and the original substrate is removed. Then the LEDs on theintermediate substrate are picked and placed one or a few at a time ontothe substrate with the control circuitry. However, this fabricationprocess is inefficient, costly and not reliable. In addition, there areno existing manufacturing tools for mass transferring micro LEDs.Therefore new tools must be developed.

In another approach, the entire LED array with its original substrate isaligned and bonded to the control circuitry using metal bonding. Thesubstrate on which the LEDs are fabricated remains in the final product,which may cause light cross-talk. Additionally, the thermal mismatchbetween the two different substrates generates stress at the bondinginterface, which can cause reliability issues. Furthermore, multi-colordisplay panels typically require more LEDs and different color LEDsgrown on different substrate materials, compared with single-colordisplay panels, thus making the traditional manufacturing process evenmore complicated and inefficient.

Display technologies are becoming increasingly popular in today'scommercial electronic devices. These display panels are widely used instationary large screens such as liquid crystal display televisions (LCDTVs) and organic light emitting diode televisions (OLED TVs) as well asportable electronic devices such as laptop personal computers,smartphones, tablets and wearable electronic devices. Much ofdevelopment for the stationary large screens is directed to achieve ahigh viewing angle in order to accommodate and enable multiple audiencesto see the screen from various angles. For example, various liquidcrystal materials such as super twisted nematic (STN) and filmcompensated super twisted nematic (FSTN) have been developed to achievea large viewing angle of each and every pixel light source in a displaypanel.

However, most of the portable electronic devices are designed mainly forsingle users, and screen orientation of these portable devices should beadjusted to be the best viewing angle for the corresponding usersinstead of a large viewing angle to accommodate multiple audiences. Forexample, a suitable viewing angle for a user may be perpendicular to thescreen surface. In this case, compared with stationary large screens,light emitted at a large viewing angle is mostly wasted. Additionally,large viewing angles raise privacy concerns for portable electronicdevices used in public areas.

In addition, in a conventional projection system based on a passiveimager device, such as liquid crystal display (LCD), digital mirrordevices (DMD), and liquid crystal on silicon (LCOS), the passive imagerdevice itself does not emit light. Specifically, the conventionalprojection system projects images by optically modulating collimatedlight emitted from a light source, i.e., by either transmitting, e.g.,by an LCD panel, or reflecting, e.g., by a DMD panel, part of the lightat the pixel level. However, the part of the light that is nottransmitted or reflected is lost, which reduces the efficiency of theprojection system. Furthermore, to provide the collimated light, complexillumination optics are used to collect divergent light emitted from thelight source. The illumination optics not only cause the system to bebulky but also introduce additional optical loss into the system, whichfurther impacts the performance of the system. In a conventionalprojection system, typically less than 10% of the illumination lightgenerated by the light source is used to form the projection image.

Light-emitting diodes (LEDs) made of semiconductor materials can be usedin mono-color or full-color displays. Current displays that employ LEDs,the LEDs are usually used as the light source to provide the light to beoptically modulated by, e.g., the LCD or the DMD panel. That is, thelight emitted by the LEDs does not form images by itself. LED displaysusing LED panels including a plurality of LED dies as the imager deviceshave also been studied. In such an LED display, the LED panel is aself-emissive imager device, where each pixel can include one LED die(mono-color display) or a plurality of LED dies each of which representsone of primary colors (full-color display).

However, the light emitted by the LED dies is generated from spontaneousemission and is thus not directional, resulting in a large divergenceangle. The large divergence angle can cause various problems in amicro-LED display. On one hand, due to the large divergence angle, onlya small portion of the light emitted by the micro-LEDs can be utilized.This may significantly reduce the efficiency and brightness of amicro-LED display system. On the other hand, due to the large divergenceangle, the light emitted by one micro-LED pixel may illuminate itsadjacent pixels, resulting in light crosstalk between pixels, loss ofsharpness, and loss of contrast. Conventional solutions reducing thelarge divergence angle may not effectively handle the light emitted fromthe micro-LED as a whole, and may utilize only the central portion ofthe light emitted from the micro-LED, leaving the rest of the lightemitted at more oblique angles to be unutilized.

As such, it would be desirable to provide an LED structure for displaypanels that addresses the above-mentioned drawbacks, amongst others.

SUMMARY

There is a need for improved multi-color LED designs that improve upon,and help to address the shortcomings of conventional display systems,such as those described above. In particular, there is a need for an LEDdevice structure that can improve the brightness and resolution at thesame time while efficiently maintaining low power consumption. And thereis also a need for display panels with reduced viewing angle for betterprotection for user's privacy, or/and reduced light waste for reducedpower consumption and reduced light interference between pixels withbetter images.

The multi-color LED device described herein integrates at least threemicro-LED structures vertically stacked by placing them at differentlayers of the device structure and utilizing separate electrodes forreceiving control currents. By placing at least three LED structuresaligned along one axis as disclosed herein, the system effectivelyenhances the light illumination efficiency within a single pixel area,and at the same time, improves the resolution of the LED panel.

Pitch refers to the distance between the centers of adjacent pixels on adisplay panel. In some embodiments, the pitch can vary from about 40microns, to about 20 microns, to about 10 microns, and/or preferably toabout 5 microns or below. Many efforts have been made to reduce thepitch. A single pixel area is fixed when the pitch specification isdetermined.

The multi-color coaxial LED system described herein makes it possible toemit light with a combination of different colors from a single pixelarea without using extra area to accommodate LED structures withdifferent colors. Therefore, the footprint of a single pixel issignificantly reduced and the resolution of the micro-LED panel can beimproved. While the concentration of the different-colored light fromone micro-LED device boundary greatly enhances the brightness within asingle pixel area.

Compared to conventional fabrication processes for micro-LED displaychips, which rely on inefficient pick and place processes or unreliablemultiple substrates approaches, the multi-color micro-LED fabricationprocesses disclosed herein effectively increases the efficiency andreliability of the micro-LED device fabrication. For example, the LEDstructures can be directly bonded on the substrate with the pixeldrivers without introducing an intermediate substrate, which cansimplify the fabrication steps and thus enhance the reliability andperformance of the LED chip. In addition, no substrate for the micro-LEDstructures remain in the final multi-color device so that cross-talk andmismatch can be reduced. In addition, planarization is applied to eitherone of the LED structures within the multi-color micro-LED or applied tothe whole multi-color micro-LED, thus allowing direct bonding orformation of different LED structures and/or other layers together withless destruction to the existing structures within the planarizedlayers.

The multi-color micro-LED devices described herein can include verticallight emission, e.g., light from each of the stacked LED structures isemitted substantially vertically relative to the surface of a substrate,horizontal light emission, e.g., light from each of the stacked LEDstructures is emitted substantially or only horizontally relative to thesurface of a substrate then reflected substantially vertically by somereflective structures, or any combination thereof. Since verticallyemitted light needs to pass through all the different layers within themulti-color micro-LED device, various layers of improving lighttransmission and light reflection are implemented. Compared with thevertical light emission, light emitted horizontally from each of thestacked LED structures does not need to pass through all the layersabove a particular structure. Therefore, horizontal light emission mayhave better light transmission efficiency and result in better lightdistinctiveness.

Various embodiments include a display panel with integrated micro-lensarray. The display panel typically includes an array of pixel lightsources (e.g., LEDs, OLEDs) electrically coupled to corresponding pixeldriver circuits (e.g., FETs). The array of micro-lenses is aligned tothe pixel light sources and positioned to reduce the divergence of lightproduced by the pixel light sources. The display panel may also includean integrated optical spacer to maintain the positioning between themicro-lenses and pixel driver circuits.

The micro-lens array reduces the divergence angle of light produced bythe pixel light sources and the useable viewing angle of the displaypanel. This, in turn, reduces power waste, increases brightness and/orbetter protects user privacy in public areas.

A display panel with integrated micro-lens array can be fabricated usinga variety of manufacturing methods, resulting in a variety of devicedesigns. In one aspect, the micro-lens array is fabricated directly asmesas or protrusions of the substrate with the pixel light sources. Insome aspects, self-assembly, high temperature reflow, grayscale maskphotolithography, molding/imprinting/stamping, and dry etching patterntransfer are techniques that can be used to fabricate micro-lens arrays.

Other aspects include components, devices, systems, improvements,methods and processes including manufacturing methods, applications, andother technologies related to any of the above.

Some exemplary embodiments include a reflective cup disposed on thesemiconductor substrate and surrounding the light emitting region, e.g.a region where the light from the multi-color micro-LED device isemitted. The reflective cup can reduce the divergence of the lightemitted from the light emitting region, and suppress the light crosstalkbetween adjacent pixel units. For example, the reflective cup canutilize the light at oblique angles, which is more efficient incollecting and converging this light for high-brightness andpower-efficient display than conventional solutions. In addition, thereflective cup can block the light emitting from micro-LEDs in adjacentpixel units, which can effectively suppress the inter-pixel lightcrosstalk and enhance color contrast and sharpness. Exemplaryembodiments of the present disclosures can improve projection brightnessand contrast, and therefore reduce power consumption in projectionapplications. Exemplary embodiments of the present disclosures can alsoimprove the light-emission directionality of the display, and thereforeprovide user with better image quality and protect user's privacy indirect-view applications. Exemplary embodiments of the presentdisclosure can provide multiple advantages. One advantage is thatexemplary embodiments of the present disclosure can suppress inter-pixellight crosstalk and enhance brightness. Exemplary embodiments of thepresent disclosure can suppress the inter-pixel light crosstalk at asmaller pitch while enhancing brightness within a single pixel in apower-efficient manner.

In some exemplary embodiments, the single pixel multi-color LED devicemay include one or more top electrodes integrated with the reflectivecup. The top electrodes may electrically connect with the top electrodelayer. The top electrode integration with the reflective cup may makethe single pixel multi-color LED device structure more compact andsimplify the fabrication process. With the adoption of the topelectrodes, the reflective cup can perform as a common P- or N-electrodeof the single pixel multi-color LED device, and thus may offer a compactstructure of the single pixel multi-color LED device.

In some exemplary embodiments, the micro-LED-pixel unit may include amicro-lens, in addition to the reflective cup. The micro-lens may bealigned to the light emitting region and positioned to reduce thedivergence of the light emitting from the light source and decreaseusable viewing angle from the single pixel multi-color LED device. Forexample, the micro-lens may be co-axially aligned to the light emittingregion, and be positioned on the light emitting region as well as top ofthe reflective cup. Part of the light emitted from the light emittingregion can directly arrive at and pass through the micro-lens; and theother part of the light emitted from the light emitting center canarrive at and be reflected by the reflective cup and then arrive at andpass through the micro-lens. Therefore, the divergence can be reducedand the useable viewing angle can be decreased to the extent thatdisplays and panels using the single pixel multi-color LED devices maybe seen by one user perpendicular to surfaces of the displays andpanels. This, in turn, can reduce power waste and increase brightnessand/or better protects user privacy in public areas. In another example,the micro-lens may be co-axially aligned to the light emitting region,positioned on the light emitting and surrounded by the reflective cup.Part of the light emitted from the light emitting region can directlyarrive at and pass through the micro-lens; another part of the lightemitted from the light emitting center can arrive at and be reflected bythe reflective cup and then arrive at and pass through the micro-lens;and the rest of the light emitted from the light emitting center canarrive at and be reflected by the reflective cup without passing throughthe micro-lens. Therefore, the divergence can be reduced and the useableviewing angle can be decreased to the extent that displays and panelsusing the single pixel multi-color LED devices may be seen by severalusers. This can also reduce power waste, increase brightnessand/properly protect user privacy in public areas.

In some exemplary embodiments, the single pixel multi-color LED devicemay further include a spacer. The spacer may be an optically transparentlayer formed to provide a proper spacing between the micro-lens and thelight emitting region. For example, the spacer may be disposed betweenthe micro-lens and the top of the reflective cup, when the micro-lens isdisposed above the reflective cup. Thus, the light emitted from thelight emitting region can pass through the spacer and then pass throughthe micro-lens. The spacer may also fill up the area surrounded by thereflective cup to increase the refractive index of the mediumsurrounding the light emitting region. Therefore, the spacer can changethe optical path of the light emitted from the light emitting region.With the adoption of the micro-lens, the light extraction efficiency ofthe single pixel multi-color LED device can be increased to furtherenhance the brightness of, e.g., the micro-LED display panel.

In some exemplary embodiments, the single pixel multi-color LED devicemay include a stair-shaped reflective cup. The stair-shaped reflectivecup may include a cavity surrounding the light emitting region. Thecavity may be formed by a plurality of inclined surfaces surrounding thelight emitting region. Sub-cavities may be formed by the plurality ofinclined surfaces and may have different dimensions in the horizontaldirection. The stair-shaped reflective cup may be disposed on thesemiconductor substrate. The stair-shaped reflective cup can reduce thedivergence of the light emitted from the light emitting region, andsuppress the light crosstalk between adjacent pixel units. For example,the stair-shaped reflective cup can utilize the light at oblique anglesby reflecting them in different reflection directions. In addition, thestair-shaped reflective cup can block the light emitting from micro-LEDsin adjacent pixel units, which can effectively suppress the inter-pixellight crosstalk and enhance color contrast and sharpness. Exemplaryembodiments of the present disclosures can improve projection brightnessand contrast, and therefore reduce power consumption in projectionapplications. Exemplary embodiments of the present disclosures can alsoimprove the light-emission directionality of the display, and thereforeprovide user with better image quality and protect user's privacy indirect-view applications.

The multi-color micro-LED devices described herein can improvebrightness and resolution at the same time and are suitable for moderndisplay panels, especially for high definition AR devices and virtualreality (VR) glasses.

Some exemplary embodiments provide a multi-color micro light-emittingdiode (LED) pixel unit for a display panel that includes: a first colorLED structure, formed on an IC substrate, wherein the first color LEDstructure includes a first light emitting layer, and a first reflectivestructure is formed on a bottom of the first light emitting layer; afirst dielectric bonding layer having a flat top surface, covering thefirst color LED structure; a second color LED structure, formed on theflat top surface of the first dielectric bonding layer, wherein thesecond color LED structure includes a second light emitting layer, and asecond reflective structure is formed on a bottom of the second lightemitting layer; a second dielectric bonding layer having a flat topsurface, covering the second color LED structure; a top electrode layer,covering the micro-LED pixel unit and electrically contacting with thefirst color LED structure and the second color LED structure; and, theIC substrate electrically connected with the first color LED structureand the second LED structure.

Some exemplary embodiments provide a micro-LED pixel unit, thatincludes: a first color LED structure, formed on an IC substrate,wherein the first color LED structure includes a first light emittinglayer, and a first reflective structure is formed on the bottom of thefirst light emitting layer; a first dielectric bonding layer having aflat top surface, covering the first color LED structure; a second colorLED structure, formed on the flat top surface of the first dielectricbonding layer, wherein the second color LED structure includes a secondlight emitting layer, and a second reflective structure is formed on abottom of the second light emitting layer; a second dielectric bondinglayer having a flat top surface, covering the second color LEDstructure; a third color LED structure, formed on the flat top surfaceof the second dielectric bonding layer, wherein the third color LEDstructure includes a third light emitting layer and, a third reflectivestructure is formed on the bottom of the third light emitting layer; athird dielectric bonding layer having a flat top surface, covering thethird color LED structure; a top electrode layer, covering the micro-LEDpixel unit and electrically contacting with the first color LEDstructure, the second color LED structure and the third color LEDstructure; and, the IC substrate electrically connected with the firstcolor LED structure, the second LED structure and the third LEDstructure.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first dielectric bondinglayer is transparent and the second dielectric bonding layer istransparent.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first reflective structureincludes at least one first high reflectivity layer, the secondreflective structure includes at least one second high reflectivitylayer, and the third reflective structure includes at least one thirdhigh reflectivity layer; and, the reflectivity of the first highreflectivity layer, the second high reflectivity layer or the third highreflectivity layer is above 60%.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the material of the first highreflectivity layer, the second high reflectivity layer or the third highreflectivity layer is metal selected from one or more of Rh, Al, Ag, andAu.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first reflective structureincludes at least two first high reflectivity layers which havedifferent refractive indices; the second reflective structure includesat two second high reflectivity layers which have different refractiveindices; and, the third reflective structure includes at two third highreflectivity layers which have different refractive indices.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit the first reflective structurefurther includes a first transparent layer on the first highreflectivity layer; the second reflective structure further includes asecond transparent layer on the second high reflectivity layer; and, thethird reflective structure further includes a second transparent layeron the third high reflectivity layer.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first transparent layer isselected from one or more of ITO and SiO₂; the second transparent layeris selected from one or more of ITO and SiO₂; and, the third transparentlayer is selected from one or more of ITO and SiO₂.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first color LED structurefurther includes a first bottom electrode conductive contact layer, thesecond color LED structure further includes a second bottom electrodeconductive contact layer, and the third color LED structure furtherincludes a third bottom electrode conductive contact layer; the firstbottom electrode conductive contact layer is electrically connected withthe IC substrate by a first contact via at a bottom of the first bottomelectrode conductive contact layer; the second bottom electrodeconductive contact layer is electrically connected with the IC substrateby a second contact via through the first dielectric bonding layer; and,the third bottom electrode conductive contact layer is electricallyconnected with the IC substrate by a third contact via through thesecond dielectric layer and the first dielectric bonding layer.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first bottom electrodeconductive contact layer is transparent, the second bottom electrodeconductive contact layer is transparent and the third bottom electrodeconductive contact layer is transparent.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a first extended portion isextended from one side of the first light emitting layer; a secondextended portion is extended from one side of the second light emittinglayer; a third extended portion is extended from one side of the secondlight emitting layer; and, a top contact via connects the first extendedportion, the second extended portion and the third extended portion tothe top electrode layer through the second dielectric bonding layer andthe third dielectric bonding layer.

Some exemplary embodiments provide a micro-LED pixel unit, that at leastincludes: a semiconductor substrate; a light emitting region, formed onthe semiconductor substrate; and, a reflective optical isolationstructure, formed around the light emitting region, wherein the top ofthe reflective optical isolation structure is higher than the top of thelight emitting region.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a micro-lens is above the topof the light emitting region.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the top of the reflectiveoptical isolation structure is higher than that of the micro-lens.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the reflective opticalisolation structure has a top opening, the lateral area of themicro-lens is less than that of the top opening.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the lateral dimension of themicro-lens is larger than an active emitting area of the first color LEDstructure; the lateral dimension of the micro-lens is larger than anactive emitting area of the second color LED structure; and, the lateraldimension of the micro-lens is larger than an active emitting area ofthe third color LED structure.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, lateral dimensions of the firstcolor LED structure, the second color LED structure and the third colorLED structure are the same.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first LED structure, thesecond LED structure and the third LED structure have a same centeraxis.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first dielectric bondinglayer is transparent, the second dielectric bonding layer istransparent, and the third dielectric bonding layer is transparent.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a thickness of the firstreflective structure is 5 nm to 10 nm; a thickness of the secondreflective structure is 5 nm to 10 nm; a thickness of the thirdreflective structure is 5 nm to 10 nm; a thickness of the first LEDstructure is not more than 300 nm; a thickness of the second LEDstructure is not more than 300 nm; and, a thickness of the third LEDstructure is not more than 300 nm.

Some exemplary embodiments provide a multi-color micro-LED pixel unitfor a display panel that includes: a first LED structure that emits afirst color, formed on an IC substrate; a first transparent dielectricbonding layer having a first flat top surface, covering the first LEDstructure; a second LED structure that emits a second color, formed onthe first flat top surface of the first transparent dielectric bondinglayer; a second transparent dielectric bonding layer having a secondflat top surface, covering the second LED structure; and a top electrodelayer, covering the multi-color micro-LED pixel unit and electricallycontacting with the first LED structure and the second LED structure;wherein the IC substrate is electrically connected with the first LEDstructure and the second LED structure.

Some exemplary embodiments provide a micro-LED pixel unit, thatincludes: a first color LED structure, formed on an IC substrate; afirst transparent dielectric bonding layer having a flat top surface,covering the first color LED structure; a second color LED structure,formed on the flat top surface of the first transparent dielectricbonding layer; a second transparent dielectric bonding layer having aflat top surface, covering the second color LED structure; a third colorLED structure, formed on the flat top surface of the second transparentdielectric bonding layer; a third dielectric bonding layer having a flattop surface, covering the third color LED structure; a top electrodelayer, covering the micro-LED pixel unit and electrically contactingwith the first color LED structure, the second color LED structure andthe third color LED structure; and the IC substrate electricallyconnected with the first color LED structure, the second LED structureand the third LED structure.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a first reflective structure isformed at the bottom of the first color LED structure; a secondreflective structure is formed at the bottom of the second color LEDstructure; and, a third reflective structure is formed at the bottom ofthe third color LED structure.

Some exemplary embodiments provide a micro-LED pixel unit, thatincludes: an IC substrate; a light emitting region, formed on the ICsubstrate, including at least one kind of LED structure and at least adielectric bonding layer, wherein each of the dielectric bonding layerhave a flat top surface covering a surface of every LED structure; a topelectrode layer, covering the micro-LED pixel unit and electricallycontacting with the every color LED structure, wherein the IC substrateis electrically connected with every color LED structure; and, astair-shaped reflective cup structure having a cavity, surrounding thelight emitting region.

Some exemplary embodiments provide a micro-LED pixel unit, thatincludes: a semiconductor substrate; a light emitting region, formed onthe semiconductor substrate; a reflective optical isolation structure,formed around the light emitting region; and, a refractive structure,formed between the reflective optical isolation structure and the lightemitting region.

Some exemplary embodiments provide a micro-LED pixel unit, thatincludes: a semiconductor substrate; a light emitting region, formed onthe semiconductor substrate, including at least one kind of LEDstructure and at least a transparent dielectric bonding layer, whereineach of the transparent dielectric bonding layer having a flat topsurface covering a surface of every LED structure; a top electrodelayer, covering the micro-LED pixel unit and electrically contactingwith every color LED structure, wherein the IC substrate is electricallyconnected with every color LED structure; a stair-shaped reflective cupstructure, formed around the light emitting region; and, a refractivestructure, formed between the stair-shaped reflective cup structure andthe light emitting region.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the reflective cup structurehas a top opening, the lateral area of the micro-lens is less than thatof the top opening.

Some exemplary embodiments provide a micro-LED pixel unit that includes:a semiconductor substrate; a light emitting region, formed on thesemiconductor substrate; a floating reflective optical isolationstructure, surrounding the light emitting region, wherein the floatingreflective optical isolation structure is positioned at a distance abovethe semiconductor substrate.

Some exemplary embodiments provide a micro-LED pixel unit, thatincludes: a semiconductor substrate; a light emitting region, formed onthe semiconductor substrate; a reflective optical isolation structure,surrounding the light emitting region; a top electrode layer, coveringthe light emitting region and electrically connecting the reflectiveoptical isolation structure, wherein the top electrode layerelectrically contacts the reflective optical isolation structure.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, an edge of the top electrodelayer touches the reflective optical isolation structure.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the light emitting regionincludes: at least one kind of LED structure and at least a dielectricbonding layer; a top electrode layer, covering the micro-LED pixel unitand electrically contacting with every color LED structure, wherein thesemiconductor substrate is electrically connected with every color LEDstructure.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the reflective opticalisolation structure is a floating reflective structure.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the reflective opticalisolation structure is a stair-shaped reflective cup structure.

Some exemplary embodiments provide a micro-LED pixel unit, that at leastincludes: a semiconductor substrate; a light emitting region, formed onthe semiconductor substrate; a floating reflective optical isolationstructure, surrounding the light emitting region, wherein the floatingreflective optical isolation structure is positioned at a distance abovethe semiconductor substrate; and a top electrode layer, formed on top ofthe light emitting region, wherein the top electrode layer contacts withthe floating reflective optical isolation structure.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the light emitting regionincludes at least one kind of LED structure and a bonding layer at thebottom of each LED structure.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first color LED structurefurther includes a first bottom electrode conductive contact layer, thesecond color LED structure further includes a second bottom electrodeconductive contact layer; the first bottom electrode conductive contactlayer is electrically connected with the IC substrate by a first contactvia at the bottom of the first bottom electrode conductive contactlayer; the second bottom electrode conductive contact layer iselectrically connected with the IC substrate by a second contact viathrough the first dielectric bonding layer.

Some exemplary embodiments provide a micro-LED pixel unit, thatincludes: a semiconductor substrate; a light emitting region, formed onthe semiconductor substrate; a top electrode layer, covering the lightemitting region and electrically contacting with the light emittingregion; a reflective cup structure, formed around the light emittingregion, wherein the top electrode layer is electrically connected withthe reflective cup structure; the semiconductor substrate iselectrically connected with the reflective cup structure; and, arefractive structure, formed between the reflective cup structure andthe light emitting region.

Some exemplary embodiments provide a micro-LED pixel unit that includes:a semiconductor substrate; a light emitting region, formed on thesemiconductor substrate, including at least one kind of LED structureand a bonding layer at a bottom of every LED structure, wherein each LEDstructure includes a light emitting layer and a bottom reflectivestructure at a bottom of the light emitting layer; a top electrodelayer, covering the micro-LED pixel unit and electrically contactingwith every color LED structure, wherein the semiconductor substrate iselectrically connected with every color LED structure; a reflective cupstructure, formed around the light emitting region; and, a refractivestructure, formed between the reflective cup structure and the lightemitting region.

Some exemplary embodiments provide a micro-LED pixel unit that includes:a semiconductor substrate; a light emitting region, formed on thesemiconductor substrate, including at least one kind of LED structureand a bonding layer at the bottom of every LED structure, wherein theLED structure includes a light emitting layer and a reflective structureat the bottom of the light emitting layer; a top electrode layer,covering the LED structure pixel unit and electrically contacting withevery color LED structure, wherein the semiconductor substrate iselectrically connected with every color LED structure; and, a stair-likereflective cup structure, surrounding the light emitting region, thelight emitted from the sidewalls of the first light emitting layer andthe second light emitting layer along the horizontal level arriving atand being reflected upward by the stair-like reflective cup structure,wherein the top of the stair-like reflective cup structure is higherthan the top of the light emitting region.

Some exemplary embodiments provide a micro-LED pixel unit that includes:a semiconductor substrate; a light emitting region, formed on thesemiconductor substrate, including at least one kind of LED structureand a metal bonding layer at a bottom of every LED structure, whereinthe LED structure includes a light emitting layer and a reflectivestructure at a bottom of the light emitting layer; a top electrodelayer, covering the micro-LED pixel unit and electrically contactingwith every color LED structure, wherein the semiconductor substrate iselectrically connected with every color LED structure; and, a floatingreflective cup structure, surrounding the light emitting region, whereinthe floating reflective cup structure is positioned a distance from thesemiconductor substrate, the light emitted from the sidewalls of thefirst light emitting layer and the second light emitting layer along thehorizontal level arriving at and being reflected upward by the floatingreflective cup.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the bottom of the floatingreflective cup structure is higher than the top surface of thesemiconductor substrate.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the floating reflective cupstructure is a stair-shaped reflective cup structure.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first LED structure isembedded within a first planarized transparent dielectric layer.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first planarizedtransparent dielectric layer is composed of solid inorganic materials orplastic materials.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the second LED structure isembedded within a second planarized transparent dielectric layer.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the second planarizedtransparent dielectric layer is composed of solid inorganic materials orplastic materials.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first transparentdielectric bonding layer is composed of solid inorganic materials orplastic materials.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first LED structureincludes a first bottom electrode conductive contact layer formed on thebottom of the first LED structure; the second LED structure includes asecond bottom electrode conductive contact layer formed on the bottom ofthe second LED structure; the first bottom electrode conductive contactlayer is electrically connected with the IC substrate by a first contactin a first via at the bottom of the first bottom electrode conductivecontact layer; and the second bottom electrode conductive contact layeris electrically connected with the IC substrate by a second contact in asecond via through the first transparent dielectric bonding layer.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first bottom electrodeconductive contact layer is transparent, and the second bottom electrodeconductive contact layer is transparent.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first LED structureincludes a first light emitting layer; a first side portion is extendedfrom a side of the first light emitting layer; the second LED structureincludes a second light emitting layer; a second side portion isextended from a side of the second light emitting layer; and a thirdcontact in a third via connects the first side portion and the secondside portion to the top electrode layer through the second transparentdielectric bonding layer.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, an optical isolation structureis formed around the micro-LED pixel unit.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the optical isolation structureis a reflective cup.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the lateral dimension of thefirst LED structure is the same as that of the second LED structure.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first LED structure and thesecond LED structure have a same central axis.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a first reflective layer isformed at the bottom of the first LED structure; a second reflectivelayer is formed at the bottom of the second LED structure.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a thickness of the firstreflective layer is 5 to 10 nm; a thickness of the second reflectivelayer is 5 to 10 nm; a thickness of the first LED structure is not morethan 300 nm; and, a thickness of the second LED is not more than 300 nm.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a bonding metal layer is formedat the bottom of the first LED structure.

Some exemplary embodiments provide a micro-light LED pixel unit, thatincludes: a first color LED structure, formed on an IC substrate,wherein the first color LED structure includes a first light emittinglayer, and a first reflective structure is formed on a bottom of thefirst light emitting layer; a first bonding metal layer, formed at abottom of the first color LED structure, and configured to bond the ICsubstrate and the first color LED structure; a second bonding metallayer, formed on a top of the first color LED structure; a second colorLED structure, formed on the second bonding metal layer, wherein thesecond color LED structure includes a second light emitting layer, and asecond reflective structure is formed on a bottom of the second lightemitting layer; a top electrode layer, covering the first color LEDstructure and the second color LED structure and electrically contactingwith the first color LED structure and the second color LED structure,wherein the IC substrate is electrically connected with the first colorLED structure and the second color LED structure; and a reflective cup,surrounding the first color LED structure and the second color LEDstructure, light emitted from the first light emitting layer and thesecond light emitting layer in a horizontal direction arriving at andbeing reflected upward by the reflective cup.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first reflective structureincludes at least one first reflective layer and the second reflectivestructure includes at least one second reflective layer, reflectivity ofthe first reflective layer or the second reflective layer being above60%.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the material of the firstreflective layer or the second reflective layer comprises one or more ofRh, Al, Ag, or Au.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first reflective structureincludes two first reflective layers and refractive indices of the twofirst reflective layers are different, and wherein the second reflectivestructure includes two second reflective layers and refractive indicesof the two second reflective layers are different.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the two first reflective layerscomprise SiO₂ and Ti₃O₅ respectively, and the two second reflectivitylayers comprise SiO₂ and Ti₃O₅ respectively.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first reflective structurefurther includes a first transparent layer on the first reflectivelayer, and the second reflective structure further includes a secondtransparent layer on the second reflective layer.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first transparent layercomprises one or more of indium tin oxide (ITO) or SiO₂, and the secondtransparent layer comprises one or more of ITO or SiO₂.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first color LED structurefurther includes a first bottom conductive contact layer and a first topconductive contact layer, and the second color LED structure furtherincludes a second bottom conductive contact layer and a second topconductive contact layer; the first light emitting layer is between thefirst bottom conductive contact layer and the first top conductivecontact layer, and the second light emitting layer is between the secondbottom conductive contact layer and the second top conductive contactlayer; the first bottom conductive contact layer is electricallyconnected with the IC substrate through the first reflective structureand the first bonding metal layer through a first contact via, and thesecond bottom conductive contact layer is electrically connected withthe IC substrate through a second contact via; and an edge of the firsttop conductive contact layer is in contact with the top electrode layer,and a top surface of the second top conductive contact layer is incontact with the top electrode layer.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the material of the reflectivecup comprises metal.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a micro-lens is formed abovethe top electrode layer.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a spacer is formed between themicro-lens and the top electrode layer.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the material of the spacercomprises silicon oxide.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the lateral dimension of themicro-lens is larger than that of an active emitting area of the firstLED structure; and the lateral dimension of the micro-lens is largerthan that of an active emitting area of the second LED structure.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first color LED structureand the second color LED structure have a same lateral dimension.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the first color LED structureand the second color LED structure have a same center axis.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a thickness of the at least onefirst reflective layer is in a range of 5 nm to 10 nm, and a thicknessof the at least one second reflective layer is in a range of 5 nm to 10nm, and wherein a thickness of the first color LED structure is not morethan 300 nm, and a thickness of the second color LED structure is notmore than 300 nm.

Some exemplary embodiments provide a micro-LED pixel unit that includes:an IC substrate; a light emitting region, formed on the IC substrate,including a plurality of color LED structures, a bottom of each of theplurality of color LED structures being connected to a correspondingbonding metal layer in the light emitting region, wherein each of theplurality of color LED structures includes a light emitting layer and areflective structure at a bottom of the light emitting layer; a topelectrode layer, covering each of the plurality of color LED structuresand electrically contacting to each of the plurality of color LEDstructures, wherein the IC substrate is electrically connected with eachof the plurality of color LED structures; and, a stair-shaped reflectivecup forming a cavity, surrounding the light emitting region, lightemitted from sidewalls of the light emitting layer of each of theplurality of color LED structures in a horizontal direction arriving atand being reflected upward by the reflective cup.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, an inner sidewall of the cavityincludes a plurality of inclined surfaces.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, angles of the plurality ofinclined surfaces relative to surface of the IC substrate from bottom totop of the cavity become smaller.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, sub-cavities formed by theplurality of inclined surfaces have different dimensions in thehorizontal direction.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, inner sidewalls of thesub-cavities are not arranged in a same plane.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the heights of the sub-cavitiesare different.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the height of a sub-cavity inmiddle of the cavity is less than the heights of other sub-cavities.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the height of a sub-cavity attop of the cavity is larger than the height of a sub-cavity at thebottom of the cavity.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the plurality of color LEDstructures further includes a top color LED structure.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the top of the cavity is higherthan the top of the top color LED structure.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the cavity includes a pluralityof sub-cavities, and each of the plurality of color LED structures is ina respectively different one of the sub-cavities.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a transparent dielectricbonding layer covers at least one of the plurality of color LEDstructures, wherein the transparent dielectric bonding layer comprisessolid inorganic materials or plastic materials.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the solid inorganic materialscomprise one or more materials selected from the group consisting ofSiO₂, Al₂O₃, Si₃N₄, Phosphosilicate glass (PSG), and Borophosphosilicateglass (BPSG).

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the plastic materials compriseone or more polymers selected from the group consisting of SU-8,PermiNex, Benzocyclobutene (BCB), and spin-on glass (SOG).

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, each of the plurality of colorLED structures includes a bottom conductive contact layer and a topconductive contact layer, and the light emitting layer is formed betweenthe bottom conductive contact layer and the top conductive contactlayer; and wherein the bottom conductive contact layer is electricallyconnected with the IC substrate through the reflective structure and thecorresponding bonding metal layer through a contact via, and, a topsurface of the top conductive contact layer of the top color LEDstructure is in contact with the top electrode layer, and an edge of thetop conductive contact layer of a color LED structure under the topcolor LED structure is in contact with the top electrode layer.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, an extended portion is extendedfrom one side of the light emitting layer of a color LED structure underthe top color LED structure, a contact via connecting the extendedportion to the top electrode layer.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the lateral dimension of themicro-lens is larger than a light emitting dimension of each of theplurality of color LED structures.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the plurality of color LEDstructures have a same center axis.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the reflective structureincludes a reflective layer and a thickness of the reflective layer isin a range of 5 nm to 10 nm, and a thickness of each of the plurality ofcolor LED structures is not more than 300 nm.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the material of the topelectrode layer is selected from the group consisting of graphene,Indium tin oxide (ITO), Aluminum-Doped Zinc Oxide (AZO), and Fluorinedoped Tin Oxide (FTO).

Some exemplary embodiments provide a micro-LED pixel unit, thatincludes: a semiconductor substrate; a light emitting region, formed onthe semiconductor substrate, including a plurality of color LEDstructures, a bottom of each of the plurality of color LED structuresbeing connected to a corresponding bonding metal layer in the lightemitting region, wherein each of the plurality of color LED structureincludes a light emitting layer and a reflective structure at a bottomof the light emitting layer; a top electrode layer, covering each of theplurality of color LED structures and electrically contacting with eachof the plurality of color LED structures, wherein the semiconductorsubstrate is electrically connected with each of the plurality of colorLED structures; a reflective cup, surrounding the light emitting region;and a refractive structure, formed between the reflective cup and thelight emitting region.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a micro-lens is formed on a topsurface of the refractive structure.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the lateral dimension of themicro-lens is not less than the lateral dimension of the light emittingregion.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the reflective cup has a topopening area, and the lateral dimension of the micro-lens is less thanthe lateral dimension of the top opening area.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a bottom dielectric layer isformed between the bottom of the reflective cup and the semiconductorsubstrate.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a top conductive layer formedon the top of the light emitting region, and the top conductive layer iselectrically connected with the reflective cup.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the top conductive layerdirectly contacts with the top of the reflective cup or the bottom ofthe reflective cup.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the top of the refractivestructure is higher than the top of the reflective cup.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the semiconductor substrate isan IC substrate.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the reflective cup is astair-shaped reflective cup forming a cavity encompassing the lightemitting region.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, sub-cavities formed by theplurality of inclined surfaces have different dimensions in thehorizontal direction.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, each of the plurality of colorLED structures includes a respective extended portion extended from oneside of the respective color LED structure, and the respective extendedportion is electrically connected with the top electrode layer via arespective first contact via, and the bottom of each of the plurality ofcolor LED structures is electrically connected with the semiconductorsubstrate via a respective second contact via.

Some exemplary embodiments provide a micro-LED pixel unit, thatincludes: a semiconductor substrate; a light emitting region, formed onthe semiconductor substrate, including a plurality of color LEDstructures, a bottom of each of the plurality of color LED structuresbeing connected to a corresponding bonding metal layer in the lightemitting region, wherein each of the plurality of color LED structuresincludes a light emitting layer and a reflective structure at a bottomof the light emitting layer; a top electrode layer, covering each of theplurality of color LED structures and electrically contacting with eachof the plurality of color LED structures, wherein the semiconductorsubstrate is electrically connected with each of the plurality of colorLED structures; and, a reflective cup, surrounding the light emittingregion, light emitted from sidewalls of the light emitting layer of eachof the plurality of color LED structures in a horizontal directionarriving at and being reflected upward by the reflective cup, a top ofthe reflective cup being higher than a top of the light emitting region.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a micro-lens is formed abovethe light emitting region.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the top of the reflective cupis higher than a top of the micro-lens.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a refractive structure is atthe bottom of the micro-lens and formed between the reflective cup andthe light emitting region.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the bottom of the lightemitting region is electrically connected with the semiconductorsubstrate.

Some exemplary embodiments provide a micro-LED pixel unit, thatincludes: a semiconductor substrate; a light emitting region, formed onthe semiconductor substrate, including a plurality of color LEDstructures, a bottom of each of the plurality of color LED structuresbeing connected to a corresponding bonding metal layer in the lightemitting region, wherein each of the plurality of color LED structuresincludes a light emitting layer and a reflective structure at a bottomof the light emitting layer; a top electrode layer, covering each of theplurality of color LED structures and electrically contacting with eachof the plurality of color LED structures, wherein the semiconductorsubstrate is electrically connected with each of the plurality of colorLED structures; and, a floating reflective cup, surrounding the lightemitting region, wherein a bottom of the floating reflective cup isabove the semiconductor substrate, light emitted from sidewalls of thelight emitting layer of each of the plurality of color LED structures ina horizontal direction arriving at and being reflected upward by thesuspended floating reflective cup.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the bottom of the floatingreflective cup is higher than a top surface of the corresponding bondingmetal layer at the bottom of one of the plurality of color LEDstructures.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the floating reflective cup isstair-shaped.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the top of the floatingreflective cup is higher than the top of the micro-lens.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a refractive structure is atthe bottom of the micro-lens and formed between the floating reflectivecup and the light emitting region.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the floating reflective cup hasa top opening area, and the lateral dimension of the micro-lens is lessthan the lateral dimension of the top opening area.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a bottom dielectric layer isformed between the floating reflective cup and the semiconductorsubstrate.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the top electrode layerdirectly contacts the top of the floating reflective cup or the bottomof the floating reflective cup.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the stair-shaped floatingreflective cup forms a cavity encompassing the light emitting region.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the material of the floatingreflective cup comprises metal.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, the reflective structureincludes a reflective layer formed at the bottom of each of theplurality of color LED structures respectively.

In some exemplary embodiments or any combination of preceding exemplaryembodiments of the micro-LED pixel unit, a thickness of the reflectivelayer is in a range of 5 nm to 10 nm, and a thickness of each of theplurality of color LED structures is not more than 300 nm.

The compact design of the multi-color LED devices and systems disclosedherein utilizes the lateral overlapping of the light emission LEDstructures, thereby improving the light emission efficiency, resolution,and overall performance of the LED display systems. Furthermore, thefabrication of the multi-color LED display systems can reliably andefficiently form the LED structure patterns without using or retainingextra substrates. In some instances, the design of the display devicesand systems disclosed herein utilizes the direct formation of themicro-lens on top of the multi-color LED devices on the substrate byutilizing the conformity of the shape of the micro-lens material to theshape of the multi-color LED device, thereby greatly reducing the stepsof the micro-lens fabrication and improving the efficiency of thedisplay panel structure formation. Reduced viewing angle and reducedlight interference improve the light emission efficiency, resolution,and overall performance of the display systems. Thus, implementation ofthe multi-color LED display systems can satisfy the rigorous displayrequirements for AR and VR, HUD, mobile device displays, wearable devicedisplays, high definition small projectors, and automotive displayscompared with the use of the conventional LEDs.

Note that the various embodiments described above can be combined withany other embodiments described herein. The features and advantagesdescribed in the specification are not all inclusive and, in particular,many additional features and advantages will be apparent to one ofordinary skill in the art in view of the drawings, specification, andclaims. Moreover, it should be noted that the language used in thespecification has been principally selected for readability andinstructional purposes, and may not have been selected to delineate orcircumscribe the inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the present disclosure can be understood in greater detail, amore particular description may be had by reference to the features ofvarious embodiments, some of which are illustrated in the appendeddrawings. The appended drawings, however, merely illustrate pertinentfeatures of the present disclosure and are therefore not to beconsidered limiting, for the description may admit to other effectivefeatures.

FIG. 1A is a top view of a single pixel tri-color LED device 100, inaccordance with some embodiments.

FIG. 1B is a cross-sectional view of a single pixel tri-color LED device100 along the diagonal line 102 in FIG. 1A, in accordance with someembodiments.

FIG. 1C is a cross-sectional view of a single pixel tri-color LED device100 along the diagonal line 150 in FIG. 1A, in accordance with someembodiments.

FIG. 2A is a cross-sectional view of a single pixel tri-color LED device100 along the diagonal line 102 in FIG. 1A with planarization, inaccordance with some embodiments.

FIG. 2B is a cross-sectional view of a single pixel tri-color LED device100 along the diagonal line 150 in FIG. 1A with planarization, inaccordance with some embodiments.

FIG. 3A is a cross-sectional view of a single pixel tri-color LED device100 with planarization along the diagonal line 102 in FIG. 1A withplanarization, in accordance with some embodiments.

FIG. 3B is a cross-sectional view of a single pixel tri-color LED device100 along the diagonal line 150 in FIG. 1A with planarization, inaccordance with some embodiments.

FIG. 4A is a top view of a single pixel tri-color LED device 400 withlayered planarization, in accordance with some embodiments.

FIG. 4B is a cross-sectional view of a single pixel tri-color LED device400 along the diagonal line 402 in FIG. 4A with layered planarization,in accordance with some embodiments.

FIG. 5 is a cross-sectional view of a single pixel tri-color LED device500 along the diagonal line 102 in FIG. 1A with a refractive structure,in accordance with some embodiments.

FIG. 6A is a cross-sectional view of a single pixel tri-color LED device600 along the diagonal line 102 in FIG. 1A with a micro-lens above areflective structure, in accordance with some embodiments.

FIG. 6B is a cross-sectional view of a single pixel tri-color LED device600 along the diagonal line 102 in FIG. 1A with a micro-lens within thearea formed by a reflective structure, in accordance with someembodiments.

FIG. 6C illustrates a fabrication method to form a display panelintegrated with a micro-lens array using top down pattern transfer,according to some embodiments.

FIG. 6D illustrates a fabrication method to form a display panelintegrated with a micro-lens array using top down pattern transfer,according to some embodiments.

FIG. 7 is a cross-sectional view 700 of three single pixel tri-color LEDdevices 710, 720 and 730 along the diagonal line such as 102 in FIG. 1Aon a substrate 104, in accordance with some embodiments.

FIG. 8 is a cross-sectional view of a single pixel tri-color LED device800 with a stair-shaped reflective cup, along the diagonal line such as402 in FIG. 4A, in accordance with some embodiments.

FIG. 9 is a cross-sectional view of a single pixel tri-color LED device900 with a floating reflective cup, along the diagonal line such as 402in FIG. 4A, in accordance with some embodiments.

FIG. 10A is a circuit diagram illustrating a matrix of single pixeltri-color LED devices 1000, in accordance with some embodiments.

FIG. 10B is a circuit diagram illustrating a matrix of single pixeltri-color LED devices 1000, in accordance with some embodiments.

FIG. 11 is a top view of a micro LED display panel 1100, in accordancewith some embodiments.

In accordance with common practice, the various features illustrated inthe drawings may not be drawn to scale. Accordingly, the dimensions ofthe various features may be arbitrarily expanded or reduced for clarity.In addition, some of the drawings may not depict all of the componentsof a given system, method or device. Finally, like reference numeralsmay be used to denote like features throughout the specification andfigures.

DETAILED DESCRIPTION

Numerous details are described herein in order to provide a thoroughunderstanding of the example embodiments illustrated in the accompanyingdrawings. However, some embodiments may be practiced without many of thespecific details, and the scope of the claims is only limited by thosefeatures and aspects specifically recited in the claims. Furthermore,well-known processes, components, and materials have not been describedin exhaustive detail so as not to unnecessarily obscure pertinentaspects of the embodiments described herein.

In some embodiments, a single pixel multi-color LED device includes twoor more LED structures. In some embodiments, each of the LED structuresincludes at least a LED light emitting layer that emits a distinctcolor. When two LED structures are within a single pixel multi-color LEDdevice, two colors and the combinations of the two colors can be emittedfrom the single pixel multi-color LED device. When three LED structuresare within a single pixel multi-color LED device, three colors and thecombinations of the three colors can be emitted from the single pixelmulti-color LED device.

In some embodiments, the light emitted from the single pixel multi-colorLED device is from the side walls of each of the LED structures withinthe single pixel multi-color LED device. In some embodiments, reflectivestructures positioned surrounding the single pixel multi-color LEDdevice to direct the light from the side walls of each of the LEDstructures upward. In some embodiments, the light emitted from thesingle pixel multi-color LED device is from the top surfaces of each ofthe LED structures within the single pixel multi-color LED device. Insome embodiments, the light emitted from the single pixel multi-colorLED device is from a combination of the side walls and top surfaces ofeach of the LED structures within the single pixel multi-color LEDdevice, for example, in a certain ratio, light from the side wallsaccounts for around 20% to 100% of the light from the single pixelmulti-color LED device.

FIG. 1A is a top view of a single pixel tri-color LED device 100, inaccordance with some embodiments.

FIG. 1B is a cross-sectional view of a single pixel tri-color LED device100 along the diagonal line 102 in FIG. 1A, in accordance with someembodiments.

FIG. 1C is a cross-sectional view of a single pixel tri-color LED device100 along the diagonal line 150 in FIG. 1A, in accordance with someembodiments.

The diagonal lines 102 and 150 each pass through the center of thesingle pixel tri-color LED device 100. The diagonal lines 102 and 150are orthogonal to each other. In some embodiments, the tri-color LEDdevice 100 includes a substrate 104. For convenience, “up” is used tomean away from the substrate 104, “down” means toward the substrate 104,and other directional terms such as top, bottom, above, below, under,beneath, etc. are interpreted accordingly. The supporting substrate 104is the substrate on which the array of individual driver circuits 106 isfabricated. In some embodiments, the driver circuits could also belocated in one of the layers above the substrate 104, or above the microtri-color LED structure 100. Each driver circuit is a pixel driver 106.In some instances, the driver circuits 106 are thin-film transistorpixel drivers or silicon CMOS pixel drivers. In one embodiment, thesubstrate 104 is a Si substrate. In another embodiment, the supportingsubstrate 104 is a transparent substrate, for example, a glasssubstrate. Other example substrates include GaAs, GaP, InP, SiC, ZnO,and sapphire substrates. The driver circuits 106 form individual pixeldrivers to control the operation of the individual single pixeltri-color LED device 100. The circuitry on substrate 104 includescontacts to each individual driver circuit 106 and also a groundcontact. As shown in both FIGS. 1A, 1B and 1C, each micro tri-color LEDstructure 100 also has two types of contacts: P-electrodes or anodes,such as 108, 126, 152, which are connected to the pixel driver 106; andN-electrodes or cathodes, such as 116, 120 and 140, which are connectedto the ground (i.e., the common electrode).

In some embodiments, the N-electrode (or N-electrodes contact pad) andits connections, such as 116, 120 and 140, are made of materials such asgraphene, ITO, Aluminum-Doped Zinc Oxide (AZO), or Fluorine doped TinOxide (FTO), or any combinations thereof. In some embodiments, theN-electrode (or N-electrodes contact pad) and its connections, such as116, 120 and 140, are made of non-transparent or transparent conductivematerials and in a preferred embodiment, transparent conductivematerials. In some embodiments, the P-electrode (or P-electrodes contactpad) and its connections, such as 126, 152, are made of materials suchas graphene, ITO, AZO, or FTO, or any combinations thereof. In someembodiments, the P-electrode (or P-electrodes contact pad) and itsconnections, such as 126, 152, are made of non-transparent ortransparent conductive materials and in a preferred embodiment,transparent conductive materials. In some embodiments, the locations ofthe P-electrodes (or P-electrodes contact pad) and its connections, andN-electrodes (or N-electrodes contact pad) and its connections can beswitched.

Although some features are described herein with the term “layer”, itshould be understood that such features are not limited to a singlelayer but may include a plurality of sublayers. In some instance, a“structure” can take the form of a “layer”.

In some embodiments, three LED structures including LED light emittinglayers 112, 130, and 136, respectively, are formed in a stackedstructure, for example, a green LED light emitting layer 130 is formedon top of a red LED light emitting layer 112, and a blue LED lightemitting layer 136 is formed on top of the green LED light emittinglayer 130.

In general, an LED light emitting layer includes a PN junction with ap-type region/layer and an n-type region/layer, and an active layerbetween the p-type region/layer and n-type region/layer.

In some embodiments, as shown in FIGS. 1A and 1B, the area of the bottomred LED light emitting layer 112 is greater than the area of the middlegreen LED light emitting layer 130. In some embodiments, the area of themiddle green LED light emitting layer 130 is greater than the area ofthe top blue LED light emitting layer 136.

In some embodiments, the light emitted from the red LED light emittinglayer 112 is able to horizontally propagate toward the sidewall of thered LED light emitting layer 112, then is reflected upward by areflective element, such as 146 and/or 148, as described below andemitted out at the top surface of the single pixel tri-color LED device100. As described below, a reflective layer 109 is positioned below thered LED light emitting layer 112 and a reflective layer 115 ispositioned above the red LED light emitting layer 112. The light emittedfrom the red LED light emitting layer 112 is reflected between the tworeflective layers 109 and 115 toward the sidewall of the red LED lightemitting layer 112.

In some embodiments, the light emitted from the green LED light emittinglayer 130 is able to horizontally propagate toward the sidewall of thegreen LED light emitting layer 130, then is reflected upward by areflective element, such as 146 and/or 148, as described below andemitted out at the top surface of the single pixel tri-color LED device100. As described below, a reflective layer 127 is positioned below thegreen LED light emitting layer 130 and a reflective layer 133 ispositioned above the green LED light emitting layer 130. The lightemitted from the green LED light emitting layer 130 is reflected betweenthe two reflective layers 127 and 133 toward the sidewall of the greenLED light emitting layer 130.

In some embodiments, the light emitted from the blue LED light emittinglayer 136 is able to horizontally propagate toward the sidewall of theblue LED light emitting layer 136, then is reflected upward by areflective element, such as 146 and/or 148, as described below andemitted out at the top surface of the single pixel tri-color LED device100. As described below, a reflective layer 135 is positioned below theblue LED light emitting layer 136. The light emitted from the blue LEDlight emitting layer 136 is reflected between the reflective layer 135and the upper surface of the blue LED light emitting layer 136 towardthe sidewall of the blue LED light emitting layer 136.

In some embodiments, the light emitted from the red LED light emittinglayer 112 is able to propagate vertically through the green LED lightemitting layer 130 and then through the blue LED light emitting layer136 to be emitted out of the tri-color LED device 100. In someembodiments, the light emitted from the green LED light emitting layer130 is able to propagate through the blue LED light emitting layer 136to be emitted out of the tri-color LED device 100. In the case ofvertical light transmission, in some embodiments, the top reflectivelayers above each of the light emitting layers, such as 115 and 133, arepreferably not included in the tri-color LED device 100. In someembodiments, light may be emitted both horizontally and verticallywithin the different LED light emitting layers.

In some embodiments, an LED light emitting layer such as 112, 130, and136 includes many epitaxial sub-layers with different compositions.Examples of the LED epitaxial layers include III-V nitride, III-Varsenide, III-V phosphide, and III-V antimonide epitaxial structures.Examples of micro LEDs include GaN based UV/blue/green micro LEDs,AlInGaP based red/orange micro LEDs, and GaAs or InP based infrared (IR)micro LEDs.

In some embodiments, each of the stacked LED structures can becontrolled individually to generate its individual light. In someembodiments, the combined light from the top LED epitaxial layer as aresult from the operations all the LED epitaxial layers in the tri-colorLED device 100 can change the color of the single pixel on a displaypanel within a small footprint.

In some embodiments, depending on the design of the LED device 100, theemitted colors of the LED structures included in the same device are notlimited to red, green and blue. For example, suitable colors can beselected from a range of different colors from a wavelength of 380 nm to700 nm in visible color range. In some embodiments, LED structuresemitting other colors from invisible range such as ultra-violet andinfrared can be implemented.

In some embodiments, when vertical light emission is combined withhorizontal light emission, for example, the three-color choice, frombottom to top can be red, green, and blue. In another embodiment, thethree-color choice, from bottom to top can be infrared, orange, andultra-violet. In some embodiments, the wavelength of the light from theLED structure on one layer of the device 100 is longer than thewavelength from the LED structure on a layer on top of the currentlayer. For instance, the wavelength of the light from the bottom LEDlight emitting layer 112 is longer than that of the middle LED lightemitting layer 130, and the wavelength of the light from the middle LEDlight emitting layer 130 is longer than that of the top LED lightemitting layer 136.

In some embodiments, when in a horizontal light emission case or whenthe portion of horizontal light emission is more than the portion ofvertical light emission from the top surface of the LED device 100, eachof the LED light emitting layers 112, 130 and 136 can be any suitablevisible or invisible color. The advantage of the horizontal lightemission is that since the light emitted does not need to go through theother top layers of the LED device 100 but from the edge or sidewall ofthe current light emitting layer directly, less light transmission lossand higher light emission efficiency can be achieved. For example,compared with the vertical light emission LED device, the horizontallight emission LED device may get 15% more, 50% more, 100% more, 150%more, or 200% more light transmission efficiency. In some instances, thelight transmission efficiency from a horizontal light emission LEDdevice can be equal to or greater than 20%, 40% or 60%.

In some embodiments, the bottom red LED light emitting layer 112 isbonded to the substrate 104 through a metal bonding layer 108. The metalbonding layer 108 may be disposed on the substrate 104. In one approach,a metal bonding layer 108 is grown on the substrate 104. In someembodiments, the metal bonding layer 108 is electrically connected toboth the driver circuit 106 on the substrate 104 and the red LED lightemitting layer 112 above the metal bonding layer 108, acting like aP-electrode. In some embodiments, the thickness of the metal bondinglayer 108 is about 0.1 micron to about 3 microns. In a preferredembodiment, the thickness of a metal bonding layer 108 is about 0.3 μm.The metal bonding layer 108 may include ohmic contact layers, and metalbonding layers. In some instances, two metal layers are included in themetal bonding layer 108. One of the metal layers is deposited the layerabove the metal bonding layer within the LED device 100. A counterpartbonding metal layer is also deposited on the substrate 104. In someembodiments, compositions for the metal bonding layer 108 include Au—Aubonding, Au—Sn bonding, Au—In bonding, Ti—Ti bonding, Cu—Cu bonding, ora mixture thereof. For example, if Au—Au bonding is selected, the twolayers of Au respectively need a Cr coating as an adhesive layer, and Ptcoating as an anti-diffusion layer. And the Pt coating is between the Aulayer and the Cr layer. The Cr and Pt layers are positioned on the topand bottom of the two bonded Au layers. In some embodiments, when thethicknesses of the two Au layers are about the same, under a highpressure and a high temperature, the mutual diffusion of Au on bothlayers bond the two layers together. Eutectic bonding, thermalcompression bonding, and transient liquid phase (TLP) bonding areexample techniques that may be used.

In some embodiments, the metal bonding layer 108 can also be used as areflector to reflect light emitted from the LED structures above.

In some embodiments, a conductive layer 110 for electrode connection isformed at the bottom of the red LED light emitting layer 112. In someembodiments, the conductive layer 110 can be a non-transparent metallayer which is not transparent to the light emitting from the LED device100. In some embodiments, the conductive layer 110 is a conductivetransparent layer, which is transparent to the light emitted from theLED device 100, such as an Indium tin oxide (ITO) layer, that is formedbetween the red LED light emitting layer 112 and the metal bonding layer108 to improve conductivity and transparency.

In some embodiments, not shown in FIG. 1A to 1C, the red LED structurehas a P-electrode contact pad 168 electrically connected to the red LEDlight emitting layer 112. In some embodiments, the P-electrode contactpad 168 is connected to the conductive layer 110. In some embodiments, aconductive layer 114 for electrode connection is formed at the top ofthe red LED light emitting layer 112. In some embodiments, theconductive layer 114 can be a metal layer or a conductive transparentlayer, such as an ITO layer, that is formed between the red LED lightemitting layer 112 and an N-electrode contact pad 116 as shown in FIG.1C to improve conductivity and transparency. In some embodiments, theN-electrode contract pad, such as 116 is made of materials such asgraphene, ITO, AZO, or FTO, or any combinations thereof.

In some embodiments, a reflective layer 109 is positioned below the redLED light emitting layer 112 between the conductive layer 110 and themetal bonding layer 108, and a reflective layer 115 is positioned abovethe red LED light emitting layer 112 between the conductive layer 114and a bonding layer 156.

In some embodiments, the red LED light emitting layer 112 has anextended portion 164 at one side of the red LED light emitting layer 112relative to the layers above it as shown in FIG. 1C. In someembodiments, the extended portion 164 is extended together with theconductive layers 110 and 114. In some embodiments, the extended portion164 is extended together with the reflective layer 109 at the bottom ofthe red LED light emitting layer 112 and the metal bonding layer 108. Insome embodiments, the red LED light emitting layer 112 is connected tothe N-electrode contact pad 116 through the extended portion of theconductive layer 114 above the extended portion 164.

In one approach, the red LED light emitting layer 112 is grown on aseparate substrate (referred to as the epitaxy substrate). The epitaxysubstrate is then removed after bonding, for example, by a laserlift-off process or wet chemical etching, leaving the structure shown inFIGS. 1B and 1C.

In some embodiments, the red LED light emitting layer 112 is for formingred micro LEDs. Examples of a red LED light emitting layer include III-Vnitride, III-V arsenide, III-V phosphide, and III-V antimonide epitaxialstructures. In some instances, films within the red LED light emittinglayer 112 can include the layers of P-type GaP/P-type AlGaInPlight-emitting layer/AlGaInP/N-type AlGaInP/N-type GaAs. In someembodiments, P type layer is generally Mg-doped, and N-type layer isgenerally Si-doped. In some examples, the thickness of the red LED lightemitting layer is about 0.1 micron to about 5 microns. In a preferredembodiment, the thickness of the red LED light emitting layer is about0.3 micron.

In some embodiments, the red LED structure includes the metal bondinglayer 108, the reflective layer 109, the conductive layer 110, the redLED light emitting layer 112, the conductive layer 114, the reflectivelayer 115, and the N-electrode contact pad 116.

In some embodiments, the bonding layer 156, is used to bond the red LEDstructure and the green LED structure together. In some embodiments, thebonding layer 156 is not transparent to the light emitted from the LEDdevice 100. In some embodiments, the materials and the thickness of thebonding layer 156 is the same as described above for the metal bondinglayer 108. In some embodiments, the bonding layer 156 can also be usedas a reflector to reflect light emitted from the LED structures above.

In some embodiments, when vertical transmission is used, the bondinglayer 156 is transparent to the light emitted from the micro LED 100. Insome embodiments, the bonding layer 156 is made of dielectric materialssuch as solid inorganic materials or plastic materials. In someembodiments, the solid inorganic materials include SiO2, Al2O3, Si3N4,Phosphosilicate glass (PSG), or Borophosphosilicate glass (BPSG), or anycombination thereof. In some embodiments, the plastic materials includepolymers such as SU-8, PermiNex, Benzocyclobutene (BCB), or transparentplastic (resin) including spin-on glass (SOG), or bonding adhesive MicroResist BCL-1200, or any combination thereof. In some embodiments, thetransparent bonding layers can facilitate the light emitted from thelayers below the bonding layers to pass through.

In some embodiments, as shown in both FIGS. 1A and 1 n FIG. 1B, thegreen LED structures has a P-electrode contact pad 126 electricallyconnected to the green LED light emitting layer 130. In someembodiments, the P-electrode contact pad 126 is connected to aconductive layer 128. In some embodiments, the conductive layer 128 forelectrode connection is formed at the bottom of the green LED lightemitting layer 130. In some embodiments, the conductive layer 128 can bea metal layer or a conductive transparent layer, such as an ITO layer,that is formed between the green LED light emitting layer 130 and aP-electrode contact pad 126 as shown in FIGS. 1A and 1B to improveconductivity and transparency.

In some embodiments, the conductive layer 128 has an extended portion128-1 at one side of the conductive layer 128 relative to the layersabove it as shown in FIG. 1B. In some embodiments, the extended portion128-1 is extended together with all the layers below the conductivelayer 128 within the LED device 100. In some embodiments, the green LEDlight emitting layer 130 is electrically connected to the P-electrodecontact pad 126 through the extended portion 128-1 of the conductivelayer 128. In some embodiments, the P-electrode contact pad 126 is alsoelectrically connected to the driver circuit 106 in the substrate 104.

In some embodiments, an insulation layer 174 made of dielectricmaterials, such as a SiO2 layer, is deposited on the surface of the LEDdevice 100. The P-electrode contact pad 126 is extended from its contactwith the driver circuit 106 to its contact with the conductive layer 128through a via or passage within the insulation layer 174. TheP-electrode contact pad 126 does not contact with other layers withinthe LED device 100.

In some embodiments, a conductive layer 132 for electrode connection isformed at the top of the green LED light emitting layer 130. In someembodiments, the conductive layer 132 can be a metal layer or aconductive transparent layer, such as an ITO layer, that is formedbetween the green LED light emitting layer 130 and an N-electrodecontact pad 120 to improve conductivity and transparency. In someembodiments, the N-electrode contract pad 120 is made of transparentconductive materials such as ITO. In some embodiments, the N-electrodecontact pad 120 is made of materials such as graphene, ITO, AZO, or FTO,or any combinations thereof.

In some embodiments, shown in FIG. 1C, the green LED structure has theN-electrode contact pad 120 electrically connected to the green LEDlight emitting layer 130. In some embodiments, the N-electrode contactpad 120 is connected to the conductive layer 132. In some embodiments,the N-electrode contact pad 120 of the green LED structure is alsoelectrically connected to the N-electrode contact pad 116 of the red LEDstructure.

As shown in FIG. 1C, in some embodiments, the green LED light emittinglayer 130 has an extended portion 166 at one side of the green LED lightemitting layer 130. In some embodiments, the extended portion 166 isextended together with the conductive layers 128 and 132 and all otherlayers below the conductive layer 128. In some embodiments, the extendedportion 166 is electrically connected to the N-electrode contact pad 120through the extended portion of the conductive layer 132 above theextended portion 166.

In some embodiments, the lateral dimension of the green LED lightemitting layer 130 is smaller than the lateral dimension of the red LEDlight emitting layer 112.

In some embodiments, a reflective layer 127 is positioned below thegreen LED light emitting layer 130 between the conductive layer 128 andthe bonding layer 156, and a reflective layer 133 is positioned abovethe green LED light emitting layer 130 between the conductive layer 132and a bonding layer 160.

In one approach, the green LED light emitting layer 130 is grown on aseparate substrate (referred to as the epitaxy substrate). The epitaxysubstrate is then removed after bonding, for example, by a laserlift-off process or wet chemical etching, leaving the structure shown inFIGS. 1B and 1C.

In some embodiments, the green LED light emitting layer 130 is forforming green micro LEDs. Examples of a green LED light emitting layerinclude III-V nitride, III-V arsenide, III-V phosphide, and III-Vantimonide epitaxial structures. In some instances, films within thegreen LED light emitting layer 130 can include the layers of P-typeGaN/InGaN light-emitting layer/N-type GaN. In some embodiments, P typeis generally Mg-doped, and N-type is generally Si-doped. In someexamples, the thickness of the green LED light emitting layer is about0.1 micron to about 5 microns. In a preferred embodiment, the thicknessof the green LED light emitting layer is about 0.3 micron.

In some embodiments, the green LED structure includes the reflectivelayer 127, the conductive layer 128, the green LED light emitting layer130, the conductive layer 132, the reflective layer 133, the P-electrodecontact pad 126, and the N-electrode contact pad 120.

In some embodiments, the first LED structure, e.g., the red LEDstructure and the second LED structure, e.g. the green LED structure,have the same central axis when the extended portions such as 164, 166,and portions below 128-1 of the conductive layer 128 are excluded. Insome embodiments, the first LED structure and the second LED structureare aligned along the same central axis when the extended portions suchas 164, 166, and portions below 128-1 of the conductive layer 128 areexcluded.

In some embodiments, the bonding layer 160, is used to bond the greenLED structure and the blue LED structure together. In some embodiments,the bonding layer 156 is not transparent to the light emitted from theLED device 100. In some embodiments, the materials and the thickness ofthe bonding layer 160 is the same as described above for the metalbonding layer 108. In some embodiments, the bonding layer 160 can alsobe used as a reflector to reflect light emitted from the LED structuresabove.

In some embodiments, when vertical transmission is used, the bondinglayer 160 is transparent to the light emitted from the LED device 100.In some embodiments, the bonding layer 160 is made of dielectricmaterials such as solid inorganic materials or plastic materials same asdescribed above for the bonding layer 156. In some embodiments, thetransparent bonding layers can facilitate the light emitted from thelayers below the bonding layers to pass through.

In some embodiments, as shown in both FIG. 1A and in FIG. 1B, the blueLED structures has a P-electrode contact pad 152 electrically connectedto the blue LED light emitting layer 136. In some embodiments, theP-electrode contact pad 152 is connected to a conductive layer 134. Insome embodiments, the conductive layer 134 for electrode connection isformed at the bottom of the blue LED light emitting layer 136. In someembodiments, the conductive layer 134 can be a metal layer or aconductive transparent layer, such as an ITO layer, that is formedbetween the blue LED light emitting layer 136 and a P-electrode contactpad 152 as shown in FIGS. 1A and 1B to improve conductivity andtransparency.

In some embodiments, the conductive layer 134 has an extended portion134-1 at one side of the conductive layer 134 relative to the layersabove it as shown in FIG. 1B. In some embodiments, the extended portion134-1 is extended together with all the layers below the conductivelayer 134 within the LED device 100. In some embodiments, the blue LEDlight emitting layer 136 is electrically connected to the P-electrodecontact pad 152 through the extended portion 134-1 of the conductivelayer 134. In some embodiments, the P-electrode contact pad 152 is alsoelectrically connected to the driver circuit 106 in the substrate 104.

In some embodiments, an insulation layer 174 made of dielectricmaterials, such as a SiO2 layer, is deposited on the surface of the LEDdevice 100. The P-electrode contact pad 152 is extended from its contactwith the driver circuit 106 to its contact with the conductive layer 134through a via or passage within the insulation layer 174. TheP-electrode contact pad 152 does not contact with other layers withinthe LED device 100.

In some embodiments, a conductive layer 138 for electrode connection isformed at the top of the blue LED light emitting layer 136. In someembodiments, the conductive layer 138 can be a metal layer or aconductive transparent layer, such as an ITO layer, that is formedbetween the blue LED light emitting layer 136 and an N-electrode contactpad 140 to improve conductivity and transparency. In some embodiments,the N-electrode contract pad 140 is made of transparent conductivematerials such as ITO. In some embodiments, the N-electrode contact pad140 is made of materials such as graphene, ITO, AZO, or FTO, or anycombinations thereof. In some embodiments, the N-electrode contact pads116, 120 and 140 are all electrically connected together as a commonN-electrode. In some embodiments, the N-electrode contact pads 116, 120and 140 are formed as one integral piece as a common N-electrode.

In some embodiments, shown in FIG. 1B, the blue LED structure has theN-electrode contact pad 140 electrically connected to the blue LED lightemitting layer 136. In some embodiments, the N-electrode contact pad 140is connected to the conductive layer 138.

In some embodiments, the lateral dimension of the blue LED lightemitting layer 136 is smaller than the lateral dimension of the greenLED light emitting layer 130.

In some embodiments, the top electrode elements, such as the N-electrodepad 140, is connected through electrical connections below the opticalisolation structures, such as 146, 148, 170 and 172. In someembodiments, the top electrode is connected through electricalconnections embedded in the substrate 104. In an example, the topelectrode 140 is connected through electrical connection elements thatis above the insulation layer 174 and below the optical isolationstructures, such as 146, 148, 170 and 172.

In some embodiments, a reflective layer 135 is positioned below the blueLED light emitting layer 136 between the conductive layer 134 and thebonding layer 160. In some embodiments, an optional reflective layer 139(not shown in FIGS. 1A-1C) is positioned above the blue LED lightemitting layer 136 on top of the conductive layer 138.

In one approach, the blue LED light emitting layer 136 is grown on aseparate substrate (referred to as the epitaxy substrate). The epitaxysubstrate is then removed after bonding, for example, by a laserlift-off process or wet chemical etching, leaving the structure shown inFIGS. 1B and 1C.

In some embodiments, the blue LED light emitting layer 136 is forforming blue micro LEDs. Examples of a blue LED light emitting layerinclude III-V nitride, III-V arsenide, III-V phosphide, and III-Vantimonide epitaxial structures. In some instances, films within theblue LED light emitting layer 136 can include the layers of P-typeGaN/InGaN light-emitting layer/N-type GaN. In some embodiments, P typeis generally Mg-doped, and N-type is generally Si-doped. In someexamples, the thickness of the blue LED light emitting layer is about0.1 micron to about 5 microns. In a preferred embodiment, the thicknessof the blue LED light emitting layer is about 0.3 micron.

In some embodiments, the blue LED structure includes the reflectivelayer 135, the conductive layer 134, the blue LED light emitting layer136, the conductive layer 138, the optional reflective layer 139, theP-electrode contact pad 152, and the N-electrode contact pad 140.

In some embodiments, the second LED structure, e.g., the green LEDstructure, and the third LED structure, e.g., the blue LED structure,have the same central axis when the extended portions such as 166, andportions below 134-1 of the conductive layer 134 are excluded. In someembodiments, the first LED structure and the second LED structure arealigned along the same central axis when the extended portions such as166, and portions below 134-1 of the conductive layer 134 are excluded.

In some embodiments, the N-electrode 140 covers the top of the tri-colorLED device 100. In some embodiments, the N-electrode 140 connects to anN-electrode in an adjacent tri-color LED device (not shown in FIG.1A-1C) via some electrical connections components, and therefore servesas a common electrode.

In some embodiments, the thickness of each of the conductive layers 110,114, 128, 132, 134, and 138 is about 0.01 micron to about 1 micron. Insome instances, before any bonding process with the next epitaxiallayer, each of the conductive layers 110, 114, 128, 132, 134, and 138 isdeposited on the respective corresponding epitaxial layer commonly byvapor deposition, for example, electron beam evaporation or sputteringdeposition. In some examples, conductive layers are used to maintain agood conductivity for electrode connection while in some instances,improving optical properties of the LED devices, such as reflectivity ortransparency.

In some embodiments, an additional dielectric layer (not shown in FIGS.1A-1C) such as a SiO₂ layer is formed above the bottom light emittinglayer 112 (and above the conductive layer 114), preferably above thereflective layer 115, and below the bonding layer 156, to electricallyseparate the N-type layer of the light emitting layer 112 from thebonding layer 156. In some embodiments, the thickness of the additionaldielectric layer is from 20 nanometers to 2 microns. In a preferredembodiment, the thickness of the additional dielectric layer is about100 nanometers. In some embodiments, an additional dielectric layer (notshown in FIGS. 1A-1C) such as a SiO₂ layer is formed above the middlelight emitting layer 130 (and above the conductive layer 132),preferably above the reflective layer 133, and below the bonding layer160, to electrically separate the N-type layer of the light emittinglayer 130 from the bonding layer 160. In some embodiments, the thicknessof the additional dielectric layer is from 20 nanometers to 2 microns.In a preferred embodiment, the thickness of the additional dielectriclayer is about 100 nanometers.

In some embodiments, in order to improve the light emission efficiencyfrom the tri-color LED device 100, optical isolation structures asfurther described below such as 146, 148, 170 and 172 are formed alongthe sidewall of the tri-color LED device 100. In some embodiments, theoptical isolation structures such as 146, 148, 170 and 172 are made fromdielectric materials such as SiO₂.

As shown in FIG. 1A from the top view, in some embodiments, thetri-color LED device 100 has a circular shape. In some embodiments, theoptical isolation structures, such as 146, 148, 170 and 172, areconnected as one piece and formed as a circular sidewall around thetri-color LED device 100. In some embodiments, the optical isolationstructures are formed as a reflective cup as described in further detailbelow. In some embodiments, the three stacked LED structures within thetri-color LED device 100 are also in circular shapes. In someembodiments, the tri-color LED device 100 can be in other shapes, suchas rectangle, square, triangle, trapezoid, polygon. In some embodiments,the optical isolation structures, such as 146, 148, 170 and 172, areconnected as one piece and formed as a sidewall around the tri-color LEDdevice 100 with other shapes such as rectangle, square, triangle,trapezoid, polygon.

As shown in FIGS. 1B and 1C, in some embodiments, the red LED lightemitting layer 112, the green LED light emitting layer 130 and the blueLED light emitting layer 136 has oblique side surfaces. As used here,the oblique side surface may refer to a surface that is notperpendicular to the top or bottom surfaces of the respective LED lightemitting layer. In some embodiments, the angle between the oblique sidewall and the bottom surface of the respective LED light emitting layeris less than 90 degrees. In some embodiments, the bonding layers 108,156 and 160 also has an oblique side surface. The oblique side surfacesmay enhance easy connections for different connectors to the LED lightemitting layers, prevent disconnections of those connectors because ofsharp angles, and enhance the overall stability of the device.

In some embodiments, the light transmission efficiency of themulti-color LED device changes as the angle of the oblique side surfaceof the LED light emitting layers relative to a normal line to thesurface of the substrate 104 changes. In some embodiments, the lighttransmission efficiency of the multi-color LED device increases as theangle of the oblique side surface of the LED light emitting layersrelative to a normal line to the surface of the substrate 104 increases.For example, when the angle of the side surface of the LED lightemitting layers relative to the normal line to the surface of thesubstrate 104 is ±5 degrees and when the optical isolation structuressuch as 146, 148, 170 and/or 172 are not reflective cups as describedbelow, the light emission efficiency of a multi-color LED device is0.32%. For example, when the angle of the side surface of the LED lightemitting layers relative to the normal line to the surface of thesubstrate 104 is ±15 degrees and when the optical isolation structuressuch as 146, 148, 170 and/or 172 are not reflective cups as describedbelow, the light emission efficiency of a multi-color LED device is2.7%. For example, when the angle of the side surface of the LED lightemitting layers relative to the normal line to the surface of thesubstrate 104 is at (for example, when the light emitting layer istilted) or very close to ±90 degrees and when the optical isolationstructures such as 146, 148, 170 and/or 172 are not reflective cups asdescribed below, the light emission efficiency of a multi-color LEDdevice is equal to or very close to 56.4%.

In contrast, the implementation of reflective cup structures, asdescribed in further detail below, improves the light transmissionefficiency of the multi-color LED device. For example, when the angle ofthe side surface of the LED light emitting layers relative to the normalline to the surface of the substrate 104 is ±5 degrees and when theoptical isolation structures such as 146, 148, 170 and/or 172 arereflective cups as described below, the light emission efficiency of amulti-color LED device is 0.65%, that is an increase of 104.6% comparedwith the LED device without a reflective cup. For example, when theangle of the side surface of the LED light emitting layers relative tothe normal line to the surface of the substrate 104 is ±15 degrees andwhen the optical isolation structures such as 146, 148, 170 and/or 172are reflective cups as described below, the light emission efficiency ofa multi-color LED device is 6.65%, that is an increase of 144.4%compared with the LED device without a reflective cup. For example, whenthe angle of the side surface of the LED light emitting layers relativeto the normal line to the surface of the substrate 104 is at (forexample, when the light emitting layer is tilted) or very close to ±90degrees and when the optical isolation structures such as 146, 148, 170and/or 172 are reflective cups as described below, the light emissionefficiency of a multi-color LED device is equal to or very close to66.65%, that is an increase of 18.4% compared with the LED devicewithout a reflective cup.

In some embodiments, reflective layers are formed above and below eachof the LED light emitting layers to improve light transmissionefficiency. As shown in both FIGS. 1B and 1C, in some embodiments, areflective layer 109 is formed between the bonding layer 108 and the redLED light emitting layer 112. In some embodiments, the reflective layer109 is formed between the bonding layer 108 and the conductive layer 110when the conductive layer 110 is present. In some embodiments, areflective layer 115 is formed between the bonding layer 156 and the redLED light emitting layer 112. In some embodiments, the reflective layer115 is formed between the bonding layer 156 and the conductive layer 114when the conductive layer 114 is present.

In some embodiments, a reflective layer 127 is formed between thebonding layer 156 and the green LED light emitting layer 130. In someembodiments, the reflective layer 127 is formed between the bondinglayer 156 and the conductive layer 128 when the conductive layer 128 ispresent. In some embodiments, a reflective layer 133 is formed betweenthe bonding layer 160 and the green LED light emitting layer 130. Insome embodiments, the reflective layer 133 is formed between the bondinglayer 160 and the conductive layer 132 when the conductive layer 132 ispresent.

In some embodiments, a reflective layer 135 is formed between thebonding layer 160 and the blue LED light emitting layer 136. In someembodiments, the reflective layer 135 is formed between the bondinglayer 160 and the conductive layer 134 when the conductive layer 134 ispresent. In some embodiments, an optional reflective layer 139 (notshown in FIGS. 1B-1C) is formed between the N-electrode pad 140 and theblue LED light emitting layer 136, while still allowing the blue LEDlight emitting layer 136 to be electrically connected to the N-electrodepad 140, for example, through a conductive path. In some embodiments,the optional reflective layer 139 is formed between the N-electrode pad140 and the conductive layer 138 when the conductive layer 138 ispresent, while still allowing the conductive layer 138 to beelectrically connected to the N-electrode pad 140, for example, througha conductive path.

In some embodiments, the materials of the reflective layers 109, 115,127, 133, 135 and 139 have a high reflectivity, especially to the lightemitted by the single pixel tri-color LED device 200. For example, thereflectivity of the reflective layers 109, 115, 127, 133, 135 and 139 isabove 60%. In another example, the reflectivity of the reflective layers109, 115, 127, 133, 135 and 139 is above 70%. In yet another example,the reflectivity of the reflective layers 109, 115, 127, 133, 135 and139 is above 80%.

In some embodiments, the material of the reflective layers 109, 115,127, 133, 135 and 139 is metal selected from one or more of Rh, Al, Ag,and Au. In some embodiments, any one of the reflective layers 109, 115,127, 133, 135 and 139 can include at least two sublayers with differentrefractive index. Each of the sublayers also has a high reflectivitysuch as above 60%, 70% or 80%.

In some embodiments, each of the reflective layers, such as 109, 115,127, 133, 135 and 139, is coated on both sides of each of the lightemitting layers such as 112, 130 and 136, or the conductive layers 110,114, 128, 132, 134, and 138, when the conductive layers are includedbefore bonding. In some instances, the thickness of each of thereflective layers such as 109, 115, 127, 133, 135 and 139, is about 2nanometers (nm) to about 5 microns. In some embodiments, the thicknessof each of the reflective layers such as 109, 115, 127, 133, 135 and139, is equal to or below 1 micron. In some preferred embodiments, thethickness of each of the reflective layers such as 109, 115, 127, 133,135 and 139, is about 5 nanometers (nm) to 10 nm.

In some embodiments, any one of the reflective layers, such as 109, 115,127, 133, 135 and 139, includes a distributed Bragg reflector (DBR)structure. For example, any one of the reflective layers, such as 109,115, 127, 133, 135 and 139, is formed from multiple layers ofalternating or different materials with varying refractive index. Insome instances, each layer boundary of the DBR structure causes apartial reflection of an optical wave. The reflective layers, such as109, 115, 127, 133, 135 and 139, can be used to reflect some selectedwavelengths, for example, reflective layers 109 and 115 for red light,reflective layers 127 and 133 for green light, and reflective layers 135and 139 for blue light. In some embodiments, any one of the reflectivelayers, such as 109, 115, 127, 133, 135 and 139, is made of multiplelayers, e.g., at least two layers, of SiO2 and Ti3O5, respectively. Byvarying the thicknesses and numbers of layers of SiO2 and Ti3O5respectively, selective reflection or transmission of light at differentwavelengths can be formed.

In some embodiments, any one of the reflective layers, such as 109, 115,127, 133, 135 and 139, further includes a transparent layer on one ofthe high reflectivity sub-layers. For example, the transparent layer,preferably formed on either side of the reflective layer, such as 109,115, 127, 133, 135 and 139, is selected from one or more of ITO andSiO₂.

In some embodiments, each of the reflective layers 109 and 115 for a redlight LED include multiple layers of Au or/and Indium Tin Oxide (ITO).

In some embodiments, each of the reflective layers 109 and 115 for a redlight LED structure has a low absorbance (for example, equal to or lessthan 25%) of the light generated by different layers of the tri-colorLED device 100. In some embodiments, each of the reflective layers 109and 115 for a red light LED structure has a high reflectance (forexample, equal to or more than 75%) of the light generated between thecurrent two reflective layers 109 and 115, for example, the red light.

In one example, the following DBR structure shown in table 1 is used toreflect green light from a green light LED:

TABLE 1 DBR layer structure for a green light LED reflective layer.Layer Layer thickness composition (in nanometer) SiO2 1000 TiO2 109.54SiO2 318.48 TiO2 64.95 SiO2 106.07 TiO2 245.76 SiO2 137.08 TiO2 65.14SiO2 106.77 TiO2 338.95 SiO2 37.27 TiO2 12.41 SiO2 352.18 TiO2 70.83SiO2 229.25 ITO 20

In some embodiments, each of the reflective layers 127 and 133 for agreen light LED structure has a low absorbance (for example, equal to orless than 25%) of the light generated by different layers of thetri-color LED device 100. In some embodiments, each of the reflectivelayers 127 and 133 for a green light LED structure has a highreflectance (for example, equal to or more than 75%) of the lightgenerated between the current two reflective layers 127 and 133, forexample, the green light.

In one example, the following DBR structure shown in table 2 is used toreflect blue light from a blue light LED:

TABLE 2 DBR layer structure for a blue light LED reflective layer. LayerLayer thickness composition (in nanometer) SiO2 1000 SiO2 183.36 TiO2 96SiO2 84.65 TiO2 51.37 SiO2 332.37 TiO2 79.95 SiO2 423.13 TiO2 52.99 SiO235.87 TiO2 235.03 SiO2 253.67 TiO2 64.38 SiO2 336.08 ITO 20

In some embodiments, each of the reflective layers 135 and optionally139 for a blue light LED structure has a low absorbance (for example,equal to or less than 25%) of the light generated by different layers ofthe tri-color LED device 100. In some embodiments, the reflective layer135 for a blue light LED structure has a high reflectance (for example,equal to or more than 75%) of the light generated above the currentreflective layer 135 or between the current reflective layers 135 and139, for example, the blue light.

FIG. 2A is a cross-sectional view of a single pixel tri-color LED device100 along the diagonal line 102 in FIG. 1A with planarization, inaccordance with some embodiments. In some embodiments, the single pixeltri-color LED device 100 has similar structures as the single pixeltri-color LED device 100 shown in FIGS. 1A, 1B and 1C with the additionof a planarized layer 176 covering the single pixel tri-color LED device100.

FIG. 2B is a cross-sectional view of a single pixel tri-color LED device100 along the diagonal line 150 in FIG. 1A with planarization, inaccordance with some embodiments. In some embodiments, the single pixeltri-color LED device 100 has similar structures as the single pixeltri-color LED device 100 shown in FIGS. 1A, 1B and 1C with the additionof a planarized layer 176 covering the single pixel tri-color LED device100.

In some embodiments, the planarized layer, such as 176, is transparentto the light emitted from the micro LED 100. In some embodiments, theplanarized layer is made of dielectric materials such as solid inorganicmaterials or plastic materials. In some embodiments, the solid inorganicmaterials include SiO2, Al2O3, Si3N4, Phosphosilicate glass (PSG), orBorophosphosilicate glass (BPSG), or any combination thereof. In someembodiments, the plastic materials include polymers such as SU-8,PermiNex, Benzocyclobutene (BCB), or transparent plastic (resin)including spin-on glass (SOG), or bonding adhesive Micro ResistBCL-1200, or any combination thereof. In some embodiments, theplanarized layer can facilitate the light emitted from the micro LED 100to pass through.

In some embodiments, the planarized layer 176 has the same height as theoptical isolation structures, for example 146, 148, 170 and 172,relative to the surface of the substrate 104. For example, theplanarized layer 176 covers the whole single pixel tri-color LED device100 and the sidewall of the optical isolation structures. The planarizedlayer 176 is on the same plane as the top surface of the opticalisolation structures.

FIG. 3A is a cross-sectional view of a single pixel tri-color LED device100 along the diagonal line 102 in FIG. 1A with planarization, inaccordance with some embodiments. In some embodiments, the single pixeltri-color LED device 100 has similar structures as the single pixeltri-color LED device 100 shown in FIGS. 1A, 1B and 1C with the additionof a planarized layer 178 covering the single pixel tri-color LED device100.

FIG. 3B is a cross-sectional view of a single pixel tri-color LED device100 along the diagonal line 150 in FIG. 1A with planarization, inaccordance with some embodiments. In some embodiments, the single pixeltri-color LED device 100 has similar structures as the single pixeltri-color LED device 100 shown in FIGS. 1A, 1B and 1C with the additionof a planarized layer 178 covering the single pixel tri-color LED device100.

In some embodiments, the planarized layer 178 has the same height as thetop electrode elements, for example 140. The planarized layer 178 is onthe same plane as the top surface of the top electrode elements, such asthe N-electrode pad 140. In some embodiments, the top electrodeelements, for example 140, is right on top of the planarized layer 178.The planarized layer 178 is on the same plane as the bottom surface ofthe top electrode elements, such as the N-electrode pad 140. Forexample, the planarized layer 178 covers the whole single pixeltri-color LED device 100 and a portion of the sidewall of the opticalisolation structures, for example 146, 148, 170 and 172.

Unlike the electrode connections shown in FIG. 1A-1C, where the topelectrode elements, such as the N-electrode pad 140, is connectedthrough electrical connections below the optical isolation structures,such as 146, 148, 170 and 172, in FIGS. 2A-2B, 3A-3B, the top electrodeelements, such as the N-electrode pad 140, is connected throughelectrical connections at least at the sidewall of the optical isolationstructures such as 146, 148, 170 and 172. In some embodiments, theN-electrode pad 140 is fixed through or on a surface of the opticalisolation structures, such as 146, 148, 170 and 172. The top electrodestructure can simplify the fabrication process especially with theplanarized layer and the make the single pixel tri-color LED device 100compact.

In some embodiments, an insulation layer can be deposited on the singlepixel multi-color LED device on the LED light emitting layers and otherlayers such as the conductive layers and reflective layers. Aplanarization process is then followed to even the surface of theinsulation layer that embeds the single pixel multi-color LED device.Vias for electrical connections are also formed within the planarizedlayers. Compared with some other processes without planarized insulationlayers, the features and layers within the planarized LED structures arebetter protected and less susceptible to the outside destruction force.Furthermore, the planarized surface can improve the light transmissionefficiency by reducing deflection from an uneven surface.

In some embodiments, through dry etching and wet etching, a tri-colorLED structure is formed and the axes of LED structures of differentcolors are aligned with one another vertically. In some embodiments, theLED structures of different colors share the same axis.

In some embodiments, each of the LED structures of different colors forma pyramid like shape or a trapezoidal cross-sectional shape. Each layerhas a narrower width or smaller area compared to a layer beneath it. Inthis instance, the width or area is measured by the dimensions of aplane parallel to the surface of the substrate 104.

In some embodiments, each of the LED structures of different colors arebonded together by bonding layers that only cover the area of the LEDstructures without extension beyond the area of the LED structures, thewhole multi-color LED device, forms a pyramid (or inverted cone) likeshape or a trapezoidal cross-sectional shape (as shown in FIGS. 1-3). Insome embodiments, the lateral dimension of the bottom LED structure, forexample, the red LED structure, can be the longest, and the lateraldimension of the top LED structure, for example, the blue LED structure,can be the shortest. A pyramid like shape can be formed naturally wheneach of the layers within the LED device is etched and patterned frombottom up. A pyramid like structure can improve the electronicconnections between the individual LED structures and to the electrodes,and simplify the fabrication process. For example, the electrodeconnections are exposed in each layer for easy connection.

In some embodiments, the bottom layer such as the metal bonding layer108 has a lateral dimension of about 1 micron to about 500 microns. In apreferred embodiment, the lateral dimension of the metal bonding layer108 at the bottom of the multi-color LED device is about 1.75 microns.In some embodiments, the vertical height of the multi-color LED deviceis about 1 micron to about 500 microns. In a preferred embodiment, thevertical height of the multi-color LED device is about 1.9 microns. In apreferred embodiment, the lateral dimension of the conductive layer 138at the top of the multi-color LED device is about 1.0 micron.

In some embodiments, the aspect ratio of a cross section of a layer ofthe tri-color LED device remains substantially the same when the lateraldimension of the same layer varies. For example, when the lateraldimension of a patterned epitaxial layer is 5 microns, the thickness ofthe patterned epitaxial layer is less than a micron. In another example,when the lateral dimension of the same patterned epitaxial layerincreases, the thickness of the same patterned epitaxial layer increasesaccordingly to maintain the same aspect ratio. In some embodiments, theaspect ratio of the cross-section of the epitaxial layers and otherlayers is less than ⅕ in thickness/width.

The shape of the LED device is not limited and in some otherembodiments, the cross-sectional shape of the tri-color LED device cantake the form of other shapes, for example, a reverse trapezoid, asemi-oval, a rectangle, a parallelogram, a triangle, or a hexagon, etc.

In some embodiments, the top conductive layer 138 above the third LEDlight emitting layer 136 is patterned using photolithography andetching. In some instances, the etching method used to form the patternis dry etching, for example, inductively coupled plasma (ICP) etching,or wet etching with an ITO etching solution. In some embodiments, thesame patterning methods can apply to all the other conductive layers,including conductive layers 110, 114, 128, 132, 134, and 138 within thetri-color LED device 100.

In some embodiments, the blue LED light emitting layer 136 and the greenLED light emitting layer 130 are patterned using photolithography andetching. In some instances, the etching method used to form the patternis dry etching, for example, inductively coupled plasma (ICP) etching,with Cl2 and BCl3 etching gases.

In some embodiments, the bonding layers including 160 and 156 arepatterned using photolithography and etching. In some instances, theetching method used to form the pattern is dry etching, for example,inductively coupled plasma (ICP) etching, with CF4 and O2 etching gases.

In some embodiments, the reflective layers including 109, 115, 127, 133,135 and 139 are patterned using photolithography and etching. In someinstances, the etching method used to form the pattern for thereflective layers especially the DBR layers is dry etching, for example,inductively coupled plasma (ICP) etching, with CF4 and O2 etching gases,or ion beam etching (IBE) with Ar gas.

In some embodiments, the red LED light emitting layer 112 is patternedusing photolithography and etching. In some instances, the etchingmethod used to form the pattern is dry etching, for example, inductivelycoupled plasma (ICP) etching, with Cl2 and HBr etching gases.

In some embodiments, the metal bonding layer 108 is patterned usingphotolithography and etching. In some instances, the etching method usedto form the pattern is dry etching, for example, inductively coupledplasma (ICP) etching, with Cl2/BCl3/Ar etching gases, or ion beametching (IBE) with Ar gas.

In some embodiments, after each of the LED device structures ispatterned, an insulation layer, such as 174, 176, 178, is deposited onthe surface of the patterned LED structure including all the patternedlayers, side walls, and the exposed substrate. In some embodiments, theinsulation layer is made of SiO2 and/or Si3N4. In some embodiments, theinsulation layer is made of TiO2. In some embodiments, the insulationlayer is formed with composition similar to SiO2 after curing a layersuch as SOG at a high temperature. In some embodiments, the insulationlayer is made of a material that has a similar thermal coefficient ofthe layers underneath the insulation layer. The surface of theinsulation layers, such as 176 and 178, is then smoothed or planarizedby a relevant method understood by a person of ordinary skill in theart, such as chemical mechanical polishing.

In some embodiments, the insulation layers, such as 176 and 178 afterplanarization are patterned to expose the electrode contact area usingphotolithography and etching. In some instances, the etching method usedto form the pattern is dry etching, for example, inductively coupledplasma (ICP) etching, with CF4 and O2.

In some embodiments, P-electrode or anode metal pads are vapordeposited, or by other deposition method, on a suitable location of thepatterned LED structure, such as on one side and/or in vias within theplanarized insulation layer, to electrically connect the red LEDstructure, the green LED structure, and the blue LED structure.

In some embodiments, separate N-electrode or cathode metal pads arevapor deposited, or by other deposition method, on a suitable locationof the patterned LED structure, such as on one side/top and/or in viaswithin the planarized insulation layer, to electrically connect the redLED structure, the green LED structure, and the blue LED structure.

FIG. 4A is a top view of a single pixel tri-color LED device 400 withlayered planarization, in accordance with some embodiments.

FIG. 4B is a cross-sectional view of a single pixel tri-color LED device400 along the diagonal line 402 in FIG. 4A with layered planarization,in accordance with some embodiments. The diagonal line passes throughthe center of the single pixel tri-color LED device 400.

Compared with the embodiments depicted in FIGS. 1-3, the main differencein the embodiments in FIG. 4A-4B is that each of the LED structures ofdifferent colors is embedded in a respective planarized insulation layerand the planarized insulation layers with the LED structure inside arethen bonded together via some bonding layers.

In some embodiments, the tri-color LED device 400 includes a substrate404. For convenience, “up” is used to mean away from the substrate 404,“down” means toward the substrate 404, and other directional terms suchas top, bottom, above, below, under, beneath, etc. are interpretedaccordingly. The supporting substrate 404 is the substrate on which thearray of individual driver circuits 406 is fabricated. In someembodiments, the driver circuits could also be located in one of thelayers above the substrate 404, or above the micro tri-color LEDstructure 400. Each driver circuit is a pixel driver 406. In someinstances, the driver circuits 406 are thin-film transistor pixeldrivers or silicon CMOS pixel drivers. In one embodiment, the substrate404 is a Si substrate. In another embodiment, the supporting substrate404 is a transparent substrate, for example, a glass substrate. Otherexample substrates include GaAs, GaP, InP, SiC, ZnO, and sapphiresubstrates. In some embodiments, the substrate 404 is around 700 micronsthick. The driver circuits 406 form individual pixel drivers to controlthe operation of the individual single pixel tri-color LED device 400.The circuitry on substrate 404 includes contacts to each individualdriver circuit 406 and also a ground contact. As shown in both FIG. 4Aand FIG. 4B, each micro tri-color LED structure 400 also has two typesof contacts: P-electrodes or anodes, such as 450 (or 408), 452, and thecombined section 422, 424 and 426, which are connected to the pixeldriver; and N-electrodes or cathodes, such as 440, 442, 444, and thecombined section 416, 418, and 420, which are connected to the ground(i.e., the common electrode).

In some embodiments, the N-electrode (or N-electrodes contact pad) andits connections, such as 440, 442, 444, and the combined section 416,418, and 420, are made of materials such as graphene, ITO,Aluminum-Doped Zinc Oxide (AZO), or Fluorine doped Tin Oxide (FTO), orany combinations thereof. In some embodiments, the N-electrode (orN-electrodes contact pad) and its connections, such as 440, 442, 444,and the combined section 416, 418, and 420, are made of non-transparentor transparent conductive materials and in a preferred embodiment,transparent conductive materials. In some embodiments, the P-electrode(or P-electrodes contact pad) and its connections, such as 450, 452, andthe combined section 422, 424 and 426, are made of materials such asgraphene, ITO, AZO, or FTO, or any combinations thereof. In someembodiments, the P-electrode (or P-electrodes contact pad) and itsconnections, such as 450, 452, and the combined section 422, 424 and426, are made of non-transparent or transparent conductive materials andin a preferred embodiment, transparent conductive materials. In someembodiments, the locations of the P-electrodes (or P-electrodes contactpad) and its connections, and N-electrodes (or N-electrodes contact pad)and its connections can be switched.

In general, an LED light emitting layer includes a PN junction with ap-type region/layer and an n-type region/layer, and an active layerbetween the p-type region/layer and n-type region/layer.

In some embodiments, the light emitted from the red LED light emittinglayer 412 is able to horizontally propagate toward the sidewall of thered LED light emitting layer 412, then is reflected upward by areflective element, such as 446 and/or 448, as described below andemitted out at the top surface of the single pixel tri-color LED device400. As described below, a reflective layer 409 is positioned below thered LED light emitting layer 412 and a reflective layer 415 ispositioned above the red LED light emitting layer 412. The light emittedfrom the red LED light emitting layer 412 is reflected between the tworeflective layers 409 and 415 toward the sidewall of the red LED lightemitting layer 412.

In some embodiments, the light emitted from the green LED light emittinglayer 430 is able to horizontally propagate toward the sidewall of thegreen LED light emitting layer 430, then is reflected upward by areflective element, such as 446 and/or 448, as described below andemitted out at the top surface of the single pixel tri-color LED device400. As described below, a reflective layer 427 is positioned below thegreen LED light emitting layer 430 and a reflective layer 433 ispositioned above the green LED light emitting layer 430. The lightemitted from the green LED light emitting layer 430 is reflected betweenthe two reflective layers 427 and 433 toward the sidewall of the greenLED light emitting layer 430.

In some embodiments, the light emitted from the blue LED light emittinglayer 436 is able to horizontally propagate toward the sidewall of theblue LED light emitting layer 436, then is reflected upward by areflective element, such as 446 and/or 448, as described below andemitted out at the top surface of the single pixel tri-color LED device400. As described below, a reflective layer 435 is positioned below theblue LED light emitting layer 436. The light emitted from the blue LEDlight emitting layer 436 is reflected between the reflective layer 435and the upper surface of the blue LED light emitting layer 436 towardthe sidewall of the blue LED light emitting layer 436.

In some embodiments, the light emitted from the red LED light emittinglayer 412 is able to propagate vertically through the green LED lightemitting layer 430 and then through the blue LED light emitting layer436 to be emitted out of the tri-color LED device 400. In someembodiments, the light emitted from the green LED light emitting layer430 is able to propagate through the blue LED light emitting layer 436to be emitted out of the tri-color LED device 400. In the case ofvertical light transmission, in some embodiments, the top reflectivelayers above each of the light emitting layers, such as 415 and 433, arepreferably not included in the tri-color LED device 400.

In some embodiments, an LED light emitting layer such as 412, 430, and436 includes many epitaxial sub-layers with different compositions.Examples of the LED epitaxial layers include III-V nitride, III-Varsenide, III-V phosphide, and III-V antimonide epitaxial structures.Examples of micro LEDs include GaN based UV/blue/green micro LEDs,AlInGaP based red/orange micro LEDs, and GaAs or InP based infrared (IR)micro LEDs.

In some embodiments, each of the stacked LED structures can becontrolled individually to generate its individual light. In someembodiments, the combined light from the top LED epitaxial layer as aresult from the operations all the LED epitaxial layers in the tri-colorLED device 400 can change the color of the single pixel on a displaypanel within a small footprint.

In some embodiments, depending on the design of the LED device 400, theemitted colors of the LED structures included in the same device are notlimited to red, green and blue. For example, suitable colors can beselected from a range of different colors from a wavelength of 380 nm to700 nm in visible color range. In some embodiments, LED structuresemitting other colors from invisible range such as ultra-violet andinfrared can be implemented.

In some embodiments, when vertical light emission is combined withhorizontal light emission, for example, the three-color choice, frombottom to top can be red, green, and blue. In another embodiment, thethree-color choice, from bottom to top can be infrared, orange, andultra-violet. In some embodiments, the wavelength of the light from theLED structure on one layer of the device 400 is longer than thewavelength from the LED structure on a layer on top of the currentlayer. For instance, the wavelength of the light from the bottom LEDlight emitting layer 412 is longer than that of the middle LED lightemitting layer 430, and the wavelength of the light from the middle LEDlight emitting layer 430 is longer than that of the top LED lightemitting layer 436.

In some embodiments, when in a horizontal light emission case or whenthe portion of horizontal light emission is more than the portion ofvertical light emission from the top surface of the LED device 400, eachof the LED light emitting layers 412, 430 and 436 can be any suitablevisible or invisible color. The advantage of the horizontal lightemission is that since the light emitted does not need to go through theother top layers of the LED device 400 but from the edge or sidewall ofthe current light emitting layer directly, less light transmission lossand higher light emission efficiency can be achieved. For example,compared with the vertical light emission LED device, the horizontallight emission LED device may get 15% more, 50% more, 100% more, 150%more, or 200% more light transmission efficiency. In some instances, thelight transmission efficiency from a horizontal light emission LEDdevice can be equal to or greater than 20%, 40% or 60%.

In some embodiments, the bottom red LED light emitting layer 412 isbonded to the substrate 404 through a metal bonding layer 408. The metalbonding layer 408 may be disposed on the substrate 404. In one approach,a metal bonding layer 408 is grown on the substrate 404. In someembodiments, the metal bonding layer 408 is electrically connected toboth the driver circuit 406 on the substrate 404 and the red LED lightemitting layer 412 above the metal bonding layer 408, acting like aP-electrode. In some embodiments, the thickness of the metal bondinglayer 408 is about 0.1 micron to about 3 microns. In a preferredembodiment, the thickness of a metal bonding layer 408 is about 0.3 μm.The metal bonding layer 408 may include ohmic contact layers, and metalbonding layers. In some instances, two metal layers are included in themetal bonding layer 408. One of the metal layers is deposited the layerabove the metal bonding layer within the LED device 400. A counterpartbonding metal layer is also deposited on the substrate 404. In someembodiments, compositions for the metal bonding layer 408 include Au—Aubonding, Au—Sn bonding, Au—In bonding, Ti—Ti bonding, Cu—Cu bonding, ora mixture thereof. For example, if Au—Au bonding is selected, the twolayers of Au respectively need a Cr coating as an adhesive layer, and Ptcoating as an anti-diffusion layer. And the Pt coating is between the Aulayer and the Cr layer. The Cr and Pt layers are positioned on the topand bottom of the two bonded Au layers. In some embodiments, when thethicknesses of the two Au layers are about the same, under a highpressure and a high temperature, the mutual diffusion of Au on bothlayers bond the two layers together. Eutectic bonding, thermalcompression bonding, and transient liquid phase (TLP) bonding areexample techniques that may be used.

In some embodiments, the metal bonding layer 408 can also be used as areflector to reflect light emitted from the LED structures above.

In some embodiments, a conductive layer 410 for electrode connection isformed at the bottom of the red LED light emitting layer 412. In someembodiments, the conductive layer 410 is a conductive transparent layer410 transparent to the light emitted from the LED device 400, such as anIndium tin oxide (ITO) layer, that is formed between the red LED lightemitting layer 412 and the metal bonding layer 408 to improveconductivity and transparency. In some embodiments, as shown in FIG. 4Aand not shown in FIG. 4B, the red LED structure has a P-electrodecontact pad 450 electrically connected to the red LED light emittinglayer 412. In some embodiments, the P-electrode contact pad 450 isconnected to the conductive layer 410. In some embodiments, a conductivelayer 414 for electrode connection is formed at the top of the red LEDlight emitting layer 412. In some embodiments, the conductive layer 414is a conductive transparent layer 414, such as an ITO layer, that isformed between the red LED light emitting layer 412 and an N-electrodecontact pad 416 to improve conductivity and transparency.

In some embodiments, the red LED light emitting layer 412 has anextended portion 464 relative to the layers above it at one side of thered LED light emitting layer 412. In some embodiments, the extendedportion 464 is extended with the conductive layers 410 and 414. In someembodiments, the extended portion 464 is connected to the N-electrodecontact pad 416 through the extended portion of the conductive layer 414above the extended portion 464.

In some embodiments, a reflective layer 409 is positioned below the redLED light emitting layer 412 between the conductive layer 410 and themetal bonding layer 408, and a reflective layer 415 is positioned abovethe red LED light emitting layer 412 between the conductive layer 414and a bonding layer 456, and in one example, within a planarizedinsulation layer 454.

In one approach, the red LED light emitting layer 412 is grown on aseparate substrate (referred to as the epitaxy substrate). The epitaxysubstrate is then removed after bonding, for example, by a laserlift-off process or wet chemical etching, leaving the structure shown inFIG. 4B.

In some embodiments, the red LED light emitting layer 412 is for formingred micro LEDs. Examples of a red LED light emitting layer include III-Vnitride, III-V arsenide, III-V phosphide, and III-V antimonide epitaxialstructures. In some instances, films within the red LED light emittinglayer 412 can include the layers of P-type GaP/P-type AlGaInPlight-emitting layer/AlGaInP/N-type AlGaInP/N-type GaAs. In someembodiments, P type layer is generally Mg-doped, and N-type layer isgenerally Si-doped. In some examples, the thickness of the red LED lightemitting layer is about 0.1 micron to about 5 microns. In a preferredembodiment, the thickness of the red LED light emitting layer is about0.3 micron.

In some embodiments, the red LED structure includes the metal bondinglayer 408, the reflective layer 409, the conductive layer 410, the redLED light emitting layer 412, the conductive layer 414, the reflectivelayer 415, and the N-electrode contact pad 416. In some embodiments, thered LED structure is formed within a planarized insulation layer 454,for example, Silicon Dioxide (SiO2) layer. In some embodiments, theplanarized insulation layer 454 covers the whole red LED structure. Insome embodiments, the whole red LED structure is embedded within theplanarized insulation layer 454. In some embodiments, the surface of theplanarized insulation layer 454 is smoothed or planarized by the methodof chemical mechanical polishing.

In some embodiments, the planarized layer, such as 454, is transparentto the light emitted from the micro LED 400. In some embodiments, theplanarized layer is made of dielectric materials such as solid inorganicmaterials or plastic materials. In some embodiments, the solid inorganicmaterials include SiO2, Al2O3, Si3N4, Phosphosilicate glass (PSG), orBorophosphosilicate glass (BPSG), or any combination thereof. In someembodiments, the plastic materials include polymers such as SU-8,PermiNex, Benzocyclobutene (BCB), or transparent plastic (resin)including spin-on glass (SOG), or bonding adhesive Micro ResistBCL-1200, or any combination thereof. In some embodiments, theplanarized layer can facilitate the light emitted from the micro LED 400to pass through. In some embodiments, the planarized layers such as 454,468, and 462 have the same composition as the bonding layer such as 456and 460. In some embodiments, the planarized layers such as 454, 468,and 462 have different composition than the bonding layer such as 456and 460.

In some embodiments, a via or through hole is formed within theplanarized insulation layer 454 to accommodate the P-electrode contactcomponents 422 and 424 for the green LED structure. The P-electrodecontact components 422 and 424 are connected to a driver circuit 406.

In some embodiments, the bonding layer 456, is used to bond the red LEDstructure and the green LED structure together. In some embodiments, thebonding layer 456 is not transparent to the light emitted from the LEDdevice 400. In some embodiments, the materials and the thickness of thebonding layer 456 is the same as described above for the metal bondinglayer 408. In some embodiments, the bonding layer 456 can also be usedas a reflector to reflect light emitted from the LED structures above.

In some embodiments, when vertical transmission is used, the bondinglayer 456 is transparent to the light emitted from the micro LED 400. Insome embodiments, the bonding layer 456 is made of dielectric materialssuch as solid inorganic materials or plastic materials. In someembodiments, the solid inorganic materials include SiO2, Al2O3, Si3N4,Phosphosilicate glass (PSG), or Borophosphosilicate glass (BPSG), or anycombination thereof. In some embodiments, the plastic materials includepolymers such as SU-8, PermiNex, Benzocyclobutene (BCB), or transparentplastic (resin) including spin-on glass (SOG), or bonding adhesive MicroResist BCL-1200, or any combination thereof. In some embodiments, thetransparent bonding layers can facilitate the light emitted from thelayers below the bonding layers to pass through.

In some embodiments, a conductive layer 428 for electrode connection isformed at the bottom of the green LED light emitting layer 430. In someembodiments, the conductive layer 428 is a conductive transparent layer428, such as an ITO layer, that is formed between the green LED lightemitting layer 430 and the bonding layer 456 to improve conductivity andtransparency.

In some embodiments, as shown in both FIG. 4A and in FIG. 4B, the greenLED structures has a P-electrode contact pad 426 electrically connectedto the green LED light emitting layer 430. In some embodiments, theP-electrode contact pad 426 is connected to the conductive layer 428. Insome embodiments, the P-electrode contact pad 426 is also connected tothe P-electrode contact components 422 and 424 within the planarizedinsulation layer 454 through a portion of the P-electrode contact pad426 within the bonding layer 456. In some embodiments, the P-electrodecontact component 422 has a cylindrical shape. In some embodiments, theP-electrode contact component 424 has a funnel like shape with the topside narrow that matches the width of the component 422 and the bottomside wide, and this shape is to support the component 422 above it. Insome embodiments, a conductive layer 432 for electrode connection isformed at the top of the green LED light emitting layer 430. In someembodiments, the conductive layer 432 is a conductive transparent layer432, such as an ITO layer, that is formed between the green LED lightemitting layer 430 and an N-electrode contact pad 420 to improveconductivity and transparency. In some embodiments, shown in both FIG.4A and in FIG. 4B, the green LED structure has the N-electrode contactpad 420 electrically connected to the green LED light emitting layer430. In some embodiments, the N-electrode contact pad 420 is connectedto the conductive layer 432. In some embodiments, the N-electrodecontact pad 420 of the green LED structure is also electricallyconnected to the N-electrode contact pad 416 of the red LED structurethrough an N-electrode contact component 418 within the transparentbonding layer 456. In some embodiments, vias or through holes are formedwithin the bonding layer 456 to accommodate a portion of the P-electrodecontact pad 426 and the N-electrode contact component 418.

In some embodiments, the green LED light emitting layer 430 has anextended portion 466 relative to the layers above it at one side of thegreen LED light emitting layer 430. In some embodiments, the extendedportion 466 is extended with the conductive layers 428 and 432. In someembodiments, the extended portion 466 is connected to the N-electrodecontact pad 420 through the extended portion of the conductive layer 432above the extended portion 466.

In some embodiments, the lateral dimension of the green LED lightemitting layer 430 is substantially the same as the lateral dimension ofthe red LED light emitting layer 412, especially for the effective lightemitting area.

In some embodiments, a reflective layer 427 is positioned below thegreen LED light emitting layer 430 between the conductive layer 428 andthe bonding layer 456, and a reflective layer 433 is positioned abovethe green LED light emitting layer 430 between the conductive layer 432and a bonding layer 460, in one example, within a planarized insulationlayer 458.

In one approach, the green LED light emitting layer 430 is grown on aseparate substrate (referred to as the epitaxy substrate). The epitaxysubstrate is then removed after bonding, for example, by a laserlift-off process or wet chemical etching, leaving the structure shown inFIG. 4B.

In some embodiments, the green LED light emitting layer 430 is forforming green micro LEDs. Examples of a green LED light emitting layerinclude III-V nitride, III-V arsenide, III-V phosphide, and III-Vantimonide epitaxial structures. In some instances, films within thegreen LED light emitting layer 430 can include the layers of P-typeGaN/InGaN light-emitting layer/N-type GaN. In some embodiments, P typeis generally Mg-doped, and N-type is generally Si-doped. In someexamples, the thickness of the green LED light emitting layer is about0.1 micron to about 5 microns. In a preferred embodiment, the thicknessof the green LED light emitting layer is about 0.3 micron.

In some embodiments, the green LED structure includes the reflectivelayer 427, the conductive layer 428, the green LED light emitting layer430, the conductive layer 432, the reflective layer 433, and theN-electrode contact pad 420. In some embodiments, the green LEDstructure is formed within a planarized insulation layer 458. In someembodiments, the planarized insulation layer 458 covers the whole greenLED structure and a portion of the P-electrode contact pad 426. In someembodiments, the whole green LED structure is embedded within theplanarized insulation layer 458. In some embodiments, both surfaces ofthe planarized insulation layer 458 is smoothed or planarized by themethod of chemical mechanical polishing.

In some embodiments, the lateral dimension of the green LED structure issubstantially the same as the lateral dimension of the red LEDstructure. In some embodiments, the first LED structure, e.g., the redLED structure and the second LED structure, e.g. the green LEDstructure, have the same central axis when the extended portions, suchas 464 and 466, are excluded. In some embodiments, the first LEDstructure and the second LED structure are aligned along the samecentral axis when the extended portions, such as 464 and 466, areexcluded.

In some embodiments, the bonding layer 460, is used to bond the greenLED structure and the blue LED structure together. In some embodiments,the bonding layer 456 is not transparent to the light emitted from theLED device 400. In some embodiments, the materials and the thickness ofthe bonding layer 460 is the same as described above for the metalbonding layer 408. In some embodiments, the bonding layer 460 can alsobe used as a reflector to reflect light emitted from the LED structuresabove.

In some embodiments, when vertical transmission is used, the bondinglayer 460 is transparent to the light emitted from the LED device 400.In some embodiments, the bonding layer 460 is made of dielectricmaterials such as solid inorganic materials or plastic materials same asdescribed above for the bonding layer 456. In some embodiments, thetransparent bonding layers can facilitate the light emitted from thelayers below the bonding layers to pass through.

In some embodiments, a conductive layer 434 for electrode connection isformed at the bottom of the blue LED light emitting layer 436. In someembodiments, the conductive layer 434 is a conductive transparent layer434, such as an ITO layer, that is formed between the blue LED lightemitting layer 436 and the bonding layer 460 to improve conductivity andtransparency. In some embodiments, as shown in FIG. 4A and not shown inFIG. 4B, the blue LED structure has a P-electrode contact pad 452electrically connected to the blue LED light emitting layer 436. In someembodiments, the P-electrode contact pad 452 is connected to theconductive layer 434. In some embodiments, the P-electrode contact pad452 is also connected to some P-electrode contact components (not shownin FIGS. 4A and 4B), similar to 422 and 424, within the planarizedinsulation layers 454 and 458, and within the transparent bonding layers456 and 460. Those P-electrode contact components are connected to adriver circuit 406.

In some embodiments, a conductive layer 438 for electrode connection isformed at the top of the blue LED light emitting layer 436. In someembodiments, the conductive layer 438 is a conductive transparent layer438, such as an ITO layer, that is formed between the blue LED lightemitting layer 436 and an N-electrode 440 to improve conductivity andtransparency. In some embodiments, as shown in FIG. 4B, the N-electrode440 has the N-electrode contact pads 442 and 444 electrically connectedto the blue LED light emitting layer 436 through the N-electrode 440 andthe conductive layer 438. In some embodiments, the N-electrode 440 isalso electrically connected to the N-electrode contact pad 420 of thegreen LED structure. In some embodiments, the N-electrode 440 is made ofmaterials such as graphene, ITO, AZO, or FTO, or any combinationsthereof.

In some embodiments, the lateral dimension of the blue LED lightemitting layer 436 is substantially the same as the lateral dimension ofthe green LED light emitting layer 430, especially for the effectivelight emitting area.

In some embodiments, a reflective layer 435 is positioned below the blueLED light emitting layer 436 between the conductive layer 434 and thebonding layer 460. In some embodiments, an optional reflective layer 439(not shown in FIG. 4B) is positioned above the blue LED light emittinglayer 436 on top of the conductive layer 438.

In one approach, the blue LED light emitting layer 436 is grown on aseparate substrate (referred to as the epitaxy substrate). The epitaxysubstrate is then removed after bonding, for example, by a laserlift-off process or wet chemical etching, leaving the structure shown inFIG. 4B.

In some embodiments, the blue LED light emitting layer 436 is forforming blue micro LEDs. Examples of a blue LED light emitting layerinclude III-V nitride, III-V arsenide, III-V phosphide, and III-Vantimonide epitaxial structures. In some instances, films within theblue LED light emitting layer 436 can include the layers of P-typeGaN/InGaN light-emitting layer/N-type GaN. In some embodiments, P typeis generally Mg-doped, and N-type is generally Si-doped. In someexamples, the thickness of the blue LED light emitting layer is about0.1 micron to about 5 microns. In a preferred embodiment, the thicknessof the blue LED light emitting layer is about 0.3 micron.

In some embodiments, the blue LED structure includes the reflectivelayer 435, the conductive layer 434, the blue LED light emitting layer436, the conductive layer 438, and the optional reflective layer 439. Insome embodiments, the blue LED structure is formed within a planarizedinsulation layer 462. In some embodiments, the planarized insulationlayer 462 covers the whole blue LED structure. In some embodiments, thewhole blue LED structure is embedded within the planarized insulationlayer 462. In some embodiments, the bottom surface of the planarizedinsulation layer 462 is smoothed or planarized by the method of chemicalmechanical polishing.

In some embodiments, vias or through holes are formed within theplanarized insulation layer 462 and the transparent bonding layer 460 toaccommodate a portion of the N-electrode 440 to connect to theN-electrode contact pad 420 of the green LED structure.

In some embodiments, the N-electrode 440 covers the top of theplanarized insulation layer 462. In some embodiments, the N-electrode440 covers the top of the tri-color LED device 400. In some embodiments,the N-electrode 440 connects to an N-electrode in an adjacent tri-colorLED device (not shown in FIG. 4A or 4B) via the N-electrode contact pads442 and 444, and therefore serves as a common electrode.

In some embodiments, the lateral dimension of the blue LED structure issubstantially the same as the lateral dimension of the green LEDstructure. In some embodiments, the second LED structure, e.g., thegreen LED structure and the third LED structure, e.g. the blue LEDstructure, have the same central axis when the extended portions, suchas 466, are excluded. In some embodiments, the second LED structure andthe third LED structure are aligned along the same central axis when theextended portions, such as 466, are excluded.

In some embodiments, the thickness of each of the conductive layers 410,414, 428, 432, 434, and 438 is about 0.01 micron to about 1 micron. Insome instances, before any bonding process with the next epitaxiallayer, each of the conductive layers 410, 414, 428, 432, 434, and 438 isdeposited on the respective corresponding epitaxial layer commonly byvapor deposition, for example, electron beam evaporation or sputteringdeposition. In some examples, conductive layers are used to maintain agood conductivity for electrode connection while in some instances,improving optical properties of the LED devices, such as reflectivity ortransparency.

In some embodiments, in order to improve the light emission efficiencyfrom the tri-color LED device 400, optical isolation structures such as446 and 448 are formed along the sidewall of the tri-color LED device400. In some embodiments, the optical isolation structures 446 and 448are made from dielectric materials such as SiO2.

As shown in FIG. 4A from the top view, in some embodiments, thetri-color LED device 400 has a circular shape. In some embodiments, theoptical isolation structures, such as 446 and 448, are connected as onepiece and formed as a circular sidewall around the tri-color LED device400. In some embodiments, the optical isolation structures are formed asa reflective cup as described in further detail below. In someembodiments, the three stacked LED structures within the tri-color LEDdevice 400 are also in circular shapes. In some embodiments, thetri-color LED device 400 can be in other shapes, such as rectangle,square, triangle, trapezoid, polygon. In some embodiments, the opticalisolation structures, such as 446 and 448, are connected as one pieceand formed as a sidewall around the tri-color LED device 400 with othershapes such as rectangle, square, triangle, trapezoid, polygon.

As shown in FIG. 4B, in some embodiments, the red LED light emittinglayer 412, the green LED light emitting layer 430 and the blue LED lightemitting layer 436 has oblique side surfaces. As used here, the obliqueside surface may refer to a surface that is not perpendicular to the topor bottom surfaces of the respective LED light emitting layer. In someembodiments, the angle between the oblique sidewall and the bottomsurface of the respective LED light emitting layer is less than 90degrees. In some embodiments, the metal bonding layer 408 also has anoblique side surface. The oblique side surfaces may enhance easyconnections for different connectors to the LED light emitting layers,prevent disconnections of those connectors because of sharp angles, andenhance the overall stability of the device.

In some embodiments, the light transmission efficiency of themulti-color LED device changes as the angle of the oblique side surfaceof the LED light emitting layers relative to a normal line to thesurface of the substrate 404 changes. In some embodiments, the lighttransmission efficiency of the multi-color LED device increases as theangle of the oblique side surface of the LED light emitting layersrelative to a normal line to the surface of the substrate 404 increases.For example, when the angle of the side surface of the LED lightemitting layers relative to the normal line to the surface of thesubstrate 404 is ±5 degrees and when the optical isolation structuressuch as 446, and/or 448 are not reflective cups as described below, thelight emission efficiency of a multi-color LED device is 0.32%. Forexample, when the angle of the side surface of the LED light emittinglayers relative to the normal line to the surface of the substrate 404is ±15 degrees and when the optical isolation structures such as 446,and/or 448 are not reflective cups as described below, the lightemission efficiency of a multi-color LED device is 2.7%. For example,when the angle of the side surface of the LED light emitting layersrelative to the normal line to the surface of the substrate 404 is at(for example, when the light emitting layer is tilted) or very close to±90 degrees and when the optical isolation structures such as 446,and/or 448 are not reflective cups as described below, the lightemission efficiency of a multi-color LED device is equal to or veryclose to 56.4%.

In contrast, the implementation of reflective cup structures, asdescribed in further detail below, improves the light transmissionefficiency of the multi-color LED device. For example, when the angle ofthe side surface of the LED light emitting layers relative to the normalline to the surface of the substrate 404 is ±5 degrees and when theoptical isolation structures such as 446, and/or 448 are reflective cupsas described below, the light emission efficiency of a multi-color LEDdevice is 0.65%, that is an increase of 104.6% compared with the LEDdevice without a reflective cup. For example, when the angle of the sidesurface of the LED light emitting layers relative to the normal line tothe surface of the substrate 404 is ±15 degrees and when the opticalisolation structures such as 446, and/or 448 are reflective cups asdescribed below, the light emission efficiency of a multi-color LEDdevice is 6.65%, that is an increase of 144.4% compared with the LEDdevice without a reflective cup. For example, when the angle of the sidesurface of the LED light emitting layers relative to the normal line tothe surface of the substrate 404 is at (for example, when the lightemitting layer is tilted) or very close to ±90 degrees and when theoptical isolation structures such as 446, and/or 448 are reflective cupsas described below, the light emission efficiency of a multi-color LEDdevice is equal to or very close to 66.65%, that is an increase of 18.4%compared with the LED device without a reflective cup.

In some embodiments, the size of the red LED light emitting layer 412,the green LED light emitting layer 430 and the blue LED light emittinglayer 436 are similar. For example, the surface areas of the red LEDlight emitting layer 412, the green LED light emitting layer 430 and theblue LED light emitting layer 436 are substantially the same, especiallyfor the effective light emitting areas.

In some embodiments, reflective layers are formed above and below eachof the LED light emitting layers to improve light transmissionefficiency. As shown in FIG. 4B, in some embodiments, a reflective layer409 is formed between the bonding layer 408 and the red LED lightemitting layer 412. In some embodiments, the reflective layer 409 isformed between the bonding layer 408 and the conductive layer 410 whenthe conductive layer 410 is present. In some embodiments, a reflectivelayer 415 is formed between the bonding layer 456 (or/and within theplanarized insulation layer 454), and the red LED light emitting layer412. In some embodiments, a reflective layer 415 is formed between thebonding layer 456 (or/and within the planarized insulation layer 454),and the conductive layer 414 when the conductive layer 414 is present.

In some embodiments, a reflective layer 427 is formed between thebonding layer 456 (or/and within the planarized insulation layer 458),and the green LED light emitting layer 430. In some embodiments,reflective layer 427 is formed between the bonding layer 456 (or/andwithin the planarized insulation layer 458), and the conductive layer428 when the conductive layer 428 is present. In some embodiments, areflective layer 433 is formed between the bonding layer 460 (or/andwithin the planarized insulation layer 458), and the green LED lightemitting layer 430. In some embodiments, the reflective layer 433 isformed between the bonding layer 460 (or/and within the planarizedinsulation layer 458), and the conductive layer 432 when the conductivelayer 432 is present.

In some embodiments, a reflective layer 435 is formed between thebonding layer 460 (or/and within the planarized insulation layer 462),and the blue LED light emitting layer 436. In some embodiments, thereflective layer 435 is formed between the bonding layer 460 (or/andwithin the planarized insulation layer 462), and the conductive layer434 when the conductive layer 434 is present. In some embodiments, anoptional reflective layer 439 (not shown in FIG. 4B) is formed betweenthe N-electrode pad 440 and the blue LED light emitting layer 436, whilestill allowing the blue LED light emitting layer 436 to be electricallyconnected to the N-electrode pad 440, for example, through a conductivepath. In some embodiments, the optional reflective layer 439 is formedbetween the N-electrode pad 440 and the conductive layer 438 when theconductive layer 438 is present, while still allowing the conductivelayer 438 to be electrically connected to the N-electrode pad 440, forexample, through a conductive path.

In some embodiments, the materials, composition, properties andfabrication of the reflective layers are the same as described abovewith respect to FIGS. 1-3.

In some embodiments, through dry etching and wet etching, a tri-colorLED structure is formed and the axes of LED structures of differentcolors are aligned with one another vertically. In some embodiments, theLED structures of different colors share the same axis.

In some embodiments, each of the LED structures of different colors forma pyramid like shape or a trapezoidal cross-sectional shape within itsrespective planarized insulation structure. Each layer has a narrowerwidth or smaller area compared to a layer beneath it. In this instance,the width or area is measured by the dimensions of a plane parallel tothe surface of the substrate 404. In some embodiments, especially whenplanarized layered structures are used, each of the LED structures ofdifferent colors has substantially the same lateral dimension comparedwith other LED structures. When each of the LED structures havesubstantially the same area, the light emitting efficiency from thewhole LED device is improved.

In some embodiments, especially when planarized layered structures arenot used and each of the LED structures of different colors are bondedtogether by bonding layers that only cover the area of the LEDstructures without extension beyond the area of the LED structures, thewhole multi-color LED device, forms a pyramid (or inverted cone) likeshape or a trapezoidal cross-sectional shape (not shown in FIG. 4B). Insome embodiments, the lateral dimension of the bottom LED structure, forexample, the red LED structure, can be the longest, and the lateraldimension of the top LED structure, for example, the blue LED structure,can be the shortest. A pyramid like shape can be formed naturally wheneach of the layers within the LED device is etched and patterned frombottom up. A pyramid like structure can improve the electronicconnections between the individual LED structures and to the electrodes,and simplify the fabrication process. For example, the electrodeconnections are exposed in each layer for easy connection.

In some embodiments, the bottom layer such as the metal bonding layer408 has a lateral dimension of about 1 micron to about 500 microns. In apreferred embodiment, the lateral dimension of the metal bonding layer408 at the bottom of the multi-color LED device is about 2.0 microns. Insome embodiments, the vertical height of the multi-color LED device isabout 1 micron to about 500 microns. In a preferred embodiment, thevertical height of the multi-color LED device is about 1.9 microns. In apreferred embodiment, the lateral dimension of the conductive layer 438at the top of the multi-color LED device is about 1.0 micron.

In some embodiments, the aspect ratio of a cross section of a layer ofthe tri-color LED device remains substantially the same when the lateraldimension of the same layer varies. For example, when the lateraldimension of a patterned epitaxial layer is 5 microns, the thickness ofthe patterned epitaxial layer is less than a micron. In another example,when the lateral dimension of the same patterned epitaxial layerincreases, the thickness of the same patterned epitaxial layer increasesaccordingly to maintain the same aspect ratio. In some embodiments, theaspect ratio of the cross-section of the epitaxial layers and otherlayers is less than ⅕ in thickness/width.

The shape of the LED device is not limited and in some otherembodiments, the cross-sectional shape of the tri-color LED device cantake the form of other shapes, for example, a reverse trapezoid, asemi-oval, a rectangle, a parallelogram, a triangle, or a hexagon, etc.

In some embodiments, with the planarized insulation layers, such as 454,458 and 462, covering each of the LED structures of different colors,the fabrication process for the single pixel tri-color LED device issimplified and the light emission efficiency of the single pixeltri-color LED device is improved. For example, each of the LEDstructures of different colors can form on its own including theconductive layers, reflective layers and the electrode contact pads andtheir related connections within the respective planarized insulationlayer first, then the LED structures are bonded together with therespective bonding layer.

In contrast, in a process to fabricate a directly stacked tri-color LEDdevice without planarization, where the LED structures of differentcolors are bonded together with some bonding layers directly, the singlepixel tri-color LED device may be a pyramid (or inversed cone) likeshape or a trapezoidal cross-sectional shape as a result of the layer bylayer patterning (and/or etching). Thus, the effective light emittingarea for an LED structure at the bottom of the stack of the single pixeltri-color LED device is the biggest while the effective light emittingarea for an LED structure at the top of the stack is the smallest. Theunevenness of the light emitting regions among the multiple LEDstructures within the LED device can degrade its light emissionefficiency. While with the planarized layered structure, since each ofthe LED structures is fabricated within its own planarized insulationlayer, the single pixel tri-color LED device are not limited to apyramid structure as described above. Instead, the effective lightemitting area of the different LED structures within the single pixeltri-color LED device can be adjusted according to the design. In someinstance, the horizontal effective light emitting areas of the differentLED structures within the single pixel tri-color LED device aresubstantially the same to improve the light emission efficiency andeasiness for electrical connections. In some cases, compared with asimilar tri-color LED structure without planarization, the planarizedtri-color LED structure can improve light emission efficiency by atleast 5%, at least 10% or sometimes, at least 20%.

In some embodiments, when a respective epitaxy substrate is used to groweach of the LED light emitting layers as described above, an insulationlayer can be deposited on each of the epitaxy substrate covering thecorresponding LED light emitting layers and other layers such as theconductive layers and reflective layers first. A planarization processis then followed to even the surface of the insulation layer that embedsthe respective LED structure. Vias for electrical connections are alsoformed within the planarized layers before bonding.

In another embodiment, the layers of an LED structure including thebonding layer can be formed on a planarized insulation layer thatalready embeds a formed LED structure directly, followed by theformation of the planarized insulation layer to cover the current LEDstructure. Vias for electrical connections are also formed within theplanarized layer before the next LED structure is formed above thecurrent LED structure.

Compared with some other processes without planarized insulation layers,where the bonding layer contacts the top or bottom of the LED structuredirectly in order to form a device, the bonding layer can contact withthe planarized insulation layer without touching the LED structures.Thus the features and layers within each of the planarized LEDstructures are better protected and less susceptible to the outsidedestruction force. Furthermore, the planarized surface can improve thelight transmission efficiency by reducing deflection from an unevensurface.

In some embodiments, the top conductive layer 438 above the third LEDlight emitting layer 436 is patterned using photolithography andetching. In some instances, the etching method used to form the patternis dry etching, for example, inductively coupled plasma (ICP) etching,or wet etching with an ITO etching solution. In some embodiments, thesame patterning methods can apply to all the other conductive layers,including layers 410, 414, 428, 432, 434, and 438 within the tri-colorLED device 400.

In some embodiments, the blue LED light emitting layer 436 and the greenLED light emitting 430 are patterned using photolithography and etching.In some instances, the etching method used to form the pattern is dryetching, for example, inductively coupled plasma (ICP) etching, with Cl2and BCl3 etching gases.

In some embodiments, the bonding layers including 460 and 456 arepatterned using photolithography and etching. In some instances, theetching method used to form the pattern is dry etching, for example,inductively coupled plasma (ICP) etching, with CF4 and O2 etching gases.

In some embodiments, the reflective layers including 409, 415, 427, 433,435 and 439 are patterned using photolithography and etching. In someinstances, the etching method used to form the pattern for thereflective layers especially the DBR layers is dry etching, for example,inductively coupled plasma (ICP) etching, with CF4 and O2 etching gases,or ion beam etching (IBE) with Ar gas.

In some embodiments, the red LED light emitting layer 412 is patternedusing photolithography and etching. In some instances, the etchingmethod used to form the pattern is dry etching, for example, inductivelycoupled plasma (ICP) etching, with Cl2 and HBr etching gases.

In some embodiments, the metal bonding layer 408 is patterned usingphotolithography and etching. In some instances, the etching method usedto form the pattern is dry etching, for example, inductively coupledplasma (ICP) etching, with Cl2/BCl3/Ar etching gases, or ion beametching (IBE) with Ar gas.

In some embodiments, after each of the LED device structures ispatterned, an insulation layer, such as 454, 458, 462, is deposited onthe surface of the patterned LED structure including all the patternedlayers, side walls, and the exposed substrate. In some embodiments, theinsulation layer is made of SiO2 and/or Si3N4. In some embodiments, theinsulation layer is made of TiO2. In some embodiments, the insulationlayer is formed with composition similar to SiO2 after curing a layersuch as SOG at a high temperature. In some embodiments, the insulationlayer is made of a material that has a similar thermal coefficient ofthe layers underneath the insulation layer. The surface of theinsulation layer is then smoothed or planarized by a relevant methodunderstood by a person of ordinary skill in the art, such as chemicalmechanical polishing.

In some embodiments, the insulation layer after planarization ispatterned to expose the electrode contact area using photolithographyand etching. In some instances, the etching method used to form thepattern is dry etching, for example, inductively coupled plasma (ICP)etching, with CF4 and O2.

In some embodiments, P-electrode or anode metal pads are vapordeposited, or by other deposition method, on a suitable location of thepatterned LED structure, such as on one side and/or in vias within theplanarized insulation layer, to electrically connect the red LEDstructure, the green LED structure, and the blue LED structure.

In some embodiments, separate N-electrode or cathode metal pads arevapor deposited, or by other deposition method, on a suitable locationof the patterned LED structure, such as on one side/top and/or in viaswithin the planarized insulation layer, to electrically connect the redLED structure, the green LED structure, and the blue LED structure.

FIG. 5 is a cross-sectional view of a single pixel tri-color LED device500 along the diagonal line 102 in FIG. 1A with a refractive structure,in accordance with some embodiments. In some embodiments, although notall shown in FIG. 5, the single pixel tri-color LED device 500 hassimilar structures as any one of the single pixel tri-color LED devicesshown in FIGS. 1-4 with the addition of a refractive structure 502formed above the top surface of the single pixel tri-color LED device toimprove light emission efficiency. Light emitted from the single pixeltri-color LED device is emitted out through a top surface of the singlepixel tri-color LED device without the refractive structure (the lightemitting out area). In some embodiments, the top surface of therefractive structure 502 is planarized. In some embodiments, therefractive structure 502 covers and is in contract with the exposedsurface of the top electrode, such as the N-electrode 140. In someembodiments, the refractive structure 502 is formed directly on thesurface of the planarized insulation layer 176. In some embodiments, therefractive structure 502 is the same as the planarized insulation layer176 and integrated with the planarized insulation layer 176.

In some embodiments, the refractive structure 502 is formed between theoptical isolation structures, for example, a reflective cup, such as 146and 148 and the top surface of the single pixel tri-color LED devicewithout the refractive structure, i.e., the light emitting out area. Insome embodiments, the top surface of the refractive structure 502 isabove the top of the optical isolation structures. In some embodiments,the top surface of the refractive structure 502 is the same or below thetop of the optical isolation structures. In some embodiments, the topsurface of the refractive structure is above the top electrode, such asthe N-electrode 140. In some embodiments, the top surface of therefractive structure is the same or below the top electrode, such as theN-electrode 140.

In some embodiments, the refractive structure 502 changes the light pathemitted from the single pixel tri-color LED device by either making thelight emitted from the LED device more focused or more divergentaccording to the design needs.

In some embodiments, the refractive layer 502 is made of dielectricmaterials. In some embodiments, the dielectric material is transparentto the light emitted by the single pixel tri-color LED device, such assilicon oxide, silicon nitride, silicon carbide, titanium oxide,zirconium oxide, aluminum oxide, etc. In some embodiments, thedielectric material is selected from one or more polymers such as SU-8,photosensitive polyimide (PSPI), BCB, etc.

In some embodiments, the refractive layer 502 is formed directly abovethe planarized insulation layers. In some embodiments, the refractivelayer 502 is formed by deposition, sputtering, or other methods.

FIG. 6A is a cross-sectional view of a single pixel tri-color LED device600 along the diagonal line 102 in FIG. 1A with a micro-lens above areflective structure, in accordance with some embodiments.

FIG. 6B is a cross-sectional view of a single pixel tri-color LED device600 along the diagonal line 102 in FIG. 1A with a micro-lens within thearea formed by a reflective structure, in accordance with someembodiments.

In some embodiments, although not all shown in FIGS. 6A-6B, the singlepixel tri-color LED device 600 has similar structures as any one of thesingle pixel tri-color LED devices shown in FIGS. 1-5 with the additionof a micro-lens 602 formed above the top surface of the single pixeltri-color LED device to improve light emission efficiency. Light emittedfrom the single pixel tri-color LED device is emitted out through thetop surface of the single pixel tri-color LED device without themicro-lens structure (the light emitting out area). In some embodiments,the micro-lens 602 is formed directly on the surface of the planarizedinsulation layer 176. In some embodiments, the micro-lens 602 is formeddirectly on the surface of the refractive structure 502 as shown in FIG.5. In some embodiments, the micro-lens 602 covers and is in contractwith the exposed surface of the top electrode, such as the N-electrode140.

In some embodiments, an optional spacer 604 is formed on top of thelight emitting out area at the bottom of the micro-lens 602. In someembodiments, the top surface of the spacer 604 is planarized. In someembodiments, the spacer 604 is formed directly on the surface of theplanarized insulation layer 176. In some embodiments, the spacer 604 isformed directly on the surface of the refractive structure 502 as shownin FIG. 5. In some embodiments, the spacer 604 is the same as therefractive structure 502 as shown in FIG. 5 and integrated with therefractive structure 502. In some embodiments, the spacer 604 covers andis in contract with the exposed surface of the top electrode, such asthe N-electrode 140. In some embodiments, the spacer 604 is integratedwith the micro-lens 602. In some embodiments, the spacer 604 is the sameas the planarized insulation layer 176 and integrated with theplanarized insulation layer 176.

In some embodiments, the micro-lens 602 is formed between the opticalisolation structures, for example, a reflective structure or areflective cup, such as 146 and 148 and the top surface of the singlepixel tri-color LED device between the optical isolation structureswithout the micro-lens, i.e., the light emitting out area. In someembodiments, the top surface of the micro-lens 602 is above the top ofthe optical isolation structures as shown in FIG. 6A. When the topsurface of the micro-lens 602 is above the top of the reflectivestructures, such as 146 and 148, substantially all the light emittedfrom the single pixel tri-color LED device including the reflective cupcan be captured and focused by the micro-lens 602. In some embodiments,the top surface of the micro-lens 602 is the same or below the top ofthe optical isolation structures as shown in FIG. 6B. When the topsurface of the micro-lens 602 is below or at the same level as the topof the reflective structures, such as 146 and 148, at least a portion ofthe light emitted from the micro-lens 602 is further reflected by thereflective structures or reflective cup which is confined in a certainarea.

In some embodiments, the lateral dimension of the bottom of themicro-lens 602 is smaller than that of the light emitting out area. Insome embodiments, the lateral dimension of the bottom of the micro-lens602 is the same or greater than that of the light emitting out area. Insome embodiments, the lateral dimension of the bottom of the micro-lens602 is smaller than that of the top surface area of the top lightemitting layer 136. In some embodiments, the lateral dimension of thebottom of the micro-lens 602 is the same or greater than that of the topsurface area of the top light emitting layer 136.

In some embodiments, the optional spacer 604 is formed between theoptical isolation structures, for example, a reflective cup, such as 146and 148 and the top surface of the single pixel tri-color LED devicewithout the micro-lens and the spacer, i.e., the light emitting outarea. In some embodiments, the top surface of the spacer 604 is abovethe top of the optical isolation structures. In some embodiments, thetop surface of the spacer 604 is the same or below the top of theoptical isolation structures. In some embodiments, the top surface ofthe spacer 604 is above the top electrode, such as the N-electrode 140.In some embodiments, the top surface of the spacer 604 is the same orbelow the top electrode, such as the N-electrode 140. In someembodiments, the lateral dimension of the bottom of the micro-lens 602is smaller than that of the top surface of the spacer 604. In someembodiments, the lateral dimension of the bottom of the micro-lens 602is the same or greater than that of the top surface of the spacer 604.

In some embodiments, the micro-lens 602 changes the light path emittedfrom the single pixel tri-color LED device by making the light emittedfrom the LED device more focused or more divergent according to thedesign needs.

In some embodiments, the spacer 604 extends the light path emitted fromthe single pixel tri-color LED device. In some embodiments, the spacer604 changes the light path emitted from the single pixel tri-color LEDdevice by making the light emitted from the LED device more focused ormore divergent according to the design needs.

In some embodiments, the micro-lens 602 can be made from a variety ofmaterials that are transparent at the wavelengths emitted from thesingle pixel tri-color LED device. Example transparent materials for themicro-lens 602 include polymers, dielectrics and semiconductors. In someembodiments, the dielectric materials include one or more materials,such as silicon oxide, silicon nitride, silicon carbide, titanium oxide,zirconium oxide, aluminum oxide, etc. In some embodiments, themicro-lens 602 is made of photoresist.

The spacer 604 is an optically transparent layer that is formed tomaintain the position of the micro-lens 602 relative to the pixel lightsource, such as the single pixel tri-color LED device, underneath it.The spacer 604 can be made from a variety of materials that aretransparent at the wavelengths emitted from the pixel light source.Example transparent materials for the spacer 604 include polymers,dielectrics and semiconductors. In some embodiments, the dielectricmaterials include one or more materials, such as silicon oxide, siliconnitride, silicon carbide, titanium oxide, zirconium oxide, aluminumoxide, etc. In some embodiments, the spacer 604 is made of photoresist.In some embodiments, the spacer 604 and the microlens 602 have the samematerial. In some embodiments, the spacer 604 and the microlens 602 havedifferent materials.

In some embodiments, the height of the micro-lens 602 is not more than 2micrometers. In some embodiments, the height of the micro-lens 602 isnot more than 1 micrometers. In some embodiments, the height of themicro-lens 602 is not more than 0.5 micrometers. In some embodiments,the width of the micro-lens 602 is not more than 4 micrometers. In someembodiments, the width of the micro-lens 602 is not more than 3micrometers. In some embodiments, the width of the micro-lens 602 is notmore than 2 micrometers. In some embodiments, the width of themicro-lens 602 is not more than 1 micrometers. In some embodiments, theratio of the width and the height of the micro-lens 602 is more than 2.

In some embodiments, the shape of the micro-lens 602 is generallyhemisphere. In some embodiments, the center axis of the micro-lens 602is aligned with or the same as the center axis of the lens-less singlepixel tri-color LED device.

For clarity, FIGS. 6A-6B show in some embodiments, in a display panel,each of single pixel light sources such as the tri-color LED devicecorresponds to one single micro-lens 602. It should be understood that afull display panel includes an array of many individual pixels and manymicro-lenses. In addition, it may not have to be a one to onecorrespondence between micro-lenses and pixel light sources, nor a oneto one correspondence between the pixel driver circuits (not shown) andthe pixel light sources. Pixel light sources could also be made ofmultiple individual light elements, for example, single pixel LEDsconnected in parallel. In some embodiments, one micro-lens 602 can coverseveral lens-less single pixel tri-color LED device.

The individual micro-lens 602 has a positive optical power and ispositioned to reduce the divergence or viewing angle for light that isemitted from the corresponding pixel light source. In one example, thelight beam emitted from the pixel light source has an originaldivergence angle that is fairly wide. In one embodiment, the originalangle for the edge light ray of the light beam relative to a verticalaxis orthogonal to the substrate 104 is greater than 60 degrees. Thelight is bent by the micro-lens 602, so that the new edge light ray nowhas a reduced divergence angle. In one embodiment, the reduced angle isless than 30 degrees. The micro-lenses in the micro-lens array aretypically the same. Examples of micro-lenses include sphericalmicro-lenses, aspherical micro-lenses, Fresnal micro-lenses andcylindrical micro-lenses.

The micro-lens 602 typically has a flat side and a curved side. In FIG.6, the bottom of the micro-lens 602 is the flat side, and the top of themicro-lens 602 is the curved side. Typical shapes of the base of eachmicro-lens 602 include circle, square, rectangle, and hexagon. Theindividual micro-lenses in a micro-lens array of a display panel may bethe same or different: in shape, curvature, optical power, size, base,spacing, etc. In some embodiments, the micro-lens 602 conforms to theshape of the single pixel tri-color LED device. In one example, theshape of the base of the micro-lens 602 is the same as that of thesingle pixel tri-color LED device, for example, in FIGS. 6A-6B, they areboth circular. In another example, the shape of the base of themicro-lens 602 is not the same as that of the single pixel tri-color LEDdevice, for instance, the circular base of micro-lens has a same widthas the single pixel tri-color LED, but a smaller area since themicro-lens base is a circle and the base of the single pixel tri-colorLED is a square. In some embodiments, the micro-lens base area is thesmaller than the area of the pixel light source. In some embodiments,the micro-lens base area is the same or larger than the area of thepixel light source.

In some embodiments, where the micro-lens 602 is formed, the spacerlayer 604 can be formed with the micro-lens 602 in the same process withthe same material. In some embodiments, the height of the pixel lightsource is larger than, the same, or smaller than the thickness of thespacer 604 measured from the bottom of the substrate 104.

The thickness of the spacer 604 is designed to maintain the properspacing between the micro-lens 604 and the pixel light source. As oneexample, for a spacer that maintains an optical spacing between pixellight source and micro-lens that is more than a focal length of themicro-lens, an image of a single pixel is formed at a certain distance.As another example, for an optical spacer that maintains an opticalspacing between pixel light source and micro-lens that is less than afocal length of the micro-lens, a reduced divergence/viewing angle isachieved. The amount of reduction of divergence/viewing angle alsopartly depends on the thickness of the spacer 604 measured from the topsurface of the pixel light source. In some embodiments, the thickness ofthe spacer 604 measured from the top surface of the pixel light sourceis not more than 1 micrometer. In some embodiments, the thickness of thespacer 604 measured from the top surface of the pixel light source isnot more than 0.5 micrometer. In some embodiments, the thickness of thespacer 604 measured from the top surface of the pixel light source isnot more than 0.2 micrometer. In some embodiments, the thickness of thespacer 604 measured from the top surface of the pixel light source isabout 1 micrometer.

In some embodiments, a brightness enhancement effect is achieved viaintegrating a micro-lens array onto the display panel. In some examples,the brightness with the micro-lens array is 4 times the brightnesswithout the micro-lens array in the direction perpendicular to thedisplay surface, due to light concentrating effect of micro-lenses. Inalternative embodiments, the brightness enhancement factor can varyaccording to different designs of the micro-lens array and the opticalspacer. For example, a factor greater than 8 can be achieved.

In some embodiments, a first method for fabricating a micro-lensincludes a step of depositing a micro-lens material layer directly on atleast the top of the pixel light source and in direct physical contactwith the pixel light source. In some embodiments, the shape of themicro-lens material layer is conformed to the shape of the pixel lightsource and forms a hemisphere on the pixel light source. In someembodiments, the top of the pixel light source is generally flat and theshape of the formed micro-lens 602 is generally hemispheric. In someembodiments, the micro-lens material layer is deposited on the surfaceof the pixel light source, such as the planarized surface of the singlepixel tri-color LED device, directly by chemical vapor deposition (CVD)technology. In some embodiments, the deposition parameters for the CVDprocess are: the power is about 0 W to about 1000 W, the pressure isabout 100 milli-torr to about 2000 milli-torr, the temperature is around23° C. to around 500° C., the gas flow is about 0 to about 3000 sccm(standard cubic centimeters per minute), and the time is about 1 hour toabout 3 hours. In some embodiments, the material of the micro-lensmaterial layer is a dielectric material such as silicon dioxide.

In some embodiments, the first method for fabricating a micro-lensfurther includes a step of patterning the micro-lens material layer toexpose the electrode area of the substrate. In some embodiments, thestep of patterning the micro-lens material layer includes an etchingstep. In some embodiments, the etching step includes a step of forming amask on the surface of the micro-lens material. The etching step alsoincludes a step of patterning the mask via a photolithography process,thereby forming openings in the mask and exposing the micro-lensmaterial layer above the electrode area of the pixel light source. Theetching step further includes a step of etching the portions of themicro-lens material layer exposed by the openings with the maskprotection in place. In some embodiments, the exposed micro-lensmaterial layer is etched by a wet etching method.

In some embodiments, a second method for fabricating a micro-lens alsoincludes an optional step of forming a mark layer with marks foraligning to the micro-lens material layer deposited in later steps. Forexample, the mark layer is formed to align the units of the lightemitting pixels to the micro-lens material layer in order to form themicro-lens at the center of the pixel light source. In some embodiments,the mark layer is formed to align the pixel light source to the layersabove it especially the micro-lens material layer in order to form themicro-lens on the top of the pixel light source.

The second method for fabricating a micro-lens further includes a stepof depositing a micro-lens material layer directly on at least the topof one pixel light source. FIGS. 6C-6D further show a fabrication methodto form a display panel integrated with a micro-lens array using topdown pattern transfer, according to some embodiments. In someembodiments, the micro-lens material layer 645 covers the top of thepixel light source 606M as shown in FIG. 6C and the top surface of themicro-lens material layer 645 is flat. In some embodiments, themicro-lens material layer 645 is deposited on the top of the pixel lightsource array 606 by spin coating. In some embodiments, the material ofthe micro-lens material layer 645 is photoresist. In some embodiments,the material of the micro-lens material layer 645 is dielectric materialsuch as silicon oxide.

The second method for fabricating a micro-lens further includes a stepof patterning the micro-lens material layer from the top down, therebyforming at least a hemisphere in the micro-lens material layer as shownin FIGS. 6C-6D. In some embodiments, the patterning is carried outwithout passing through or etching to the bottom of the micro-lensmaterial layer 645. In some embodiments, the hemisphere of themicro-lens 620 is placed above at least one pixel light source 606M.

In some embodiments, the step of patterning the micro-lens materiallayer from the top down further includes a first step of depositing amask layer 630 on the surface of the micro-lens material layer 645 asshown in FIG. 6C.

The step of patterning the micro-lens material layer from the top downalso includes a second step of patterning the mask layer 630 to form ahemisphere pattern in the mask layer 630. In some examples, the masklayer 630 is patterned by a photolithography process firstly and then areflowing process. In some embodiments, the photo-sensitive polymer masklayer 630 is patterned into isolated cells 640, as shown in FIG. 6C indotted rectangle cells, to prepare for the formation of the hemispherepattern. As one example, the isolated cells 640 are patterned and formedvia a photo-lithography process. The patterned photo-sensitive polymermask layer 650 with the isolated cells 640 is then shaped intohemisphere pattern 660 using high temperature reflow process. In oneapproach, the isolated cells 640 are formed into isolated hemispherepattern 660 via high temperature reflow. In some embodiments, theisolated hemisphere pattern 660 of one pixel is not in direct physicalcontact with a hemisphere pattern of an adjacent pixel. In someembodiments, the hemisphere pattern 660 of one pixel only contacts witha hemisphere pattern of an adjacent pixel at the bottom of thehemisphere pattern 660. The patterned photo-sensitive polymer mask layer650 is heated to a temperature above the melting point of the polymermaterial for a certain time. After the polymer material melts into aliquefied state, the surface tension of the liquefied material willrender it into a shape with a smooth curvature surface. For a cell witha round base of a radius R when the height of the cell is 2R/3, ahemispherical shape/pattern will be formed after the reflow process.FIG. 6C shows a display panel integrated with the array of hemispherepatterns 660 after the high temperature reflow process is finished. Insome embodiments, the hemisphere pattern in the mask layer can be formedby other fabrication method including the fabrication method for themicro-lens described in the first method for fabricating a micro-lens.In some other embodiments, the hemisphere pattern in the mask layer canbe formed using grayscale mask photolithography exposure. In some otherembodiments, the hemisphere pattern in the mask layer can be formed viaa mold/imprinting process.

The step of patterning the micro-lens material layer from the top downfurther includes a third step of using the hemisphere pattern 660 as amask, etching the micro-lens material layer 645 to form the hemispherein the micro-lens material layer 645. In some examples, etching themicro-lens material layer 645 is by a photolithography process. In someexamples, etching the micro-lens material layer 645 is by a dry etchingsuch as plasma etching process 635 as shown in FIG. 6C. In someembodiments, after the micro-lens material layer 645 is etched, themicro-lens material layer 645 is not etched through to expose the topsurface of the pixel light source 606M as shown in FIGS. 6C-6D, therebya spacer 670 is formed on the top of the pixel light source 606M orcovering the top of the pixel light source 606M as shown in FIG. 6D.

The second method for fabricating a micro-lens further includes a stepof patterning the micro-lens material layer to expose the electrode area(not shown in FIG. 6D) of the substrate. In some embodiments, the stepof patterning the micro-lens material layer includes an etching step. Insome embodiments, the etching step includes a step of forming a mask onthe surface of the micro-lens material. The etching step also includes astep of patterning the mask via a photolithography process, therebyforming openings in the mask and exposing the micro-lens material layerabove the electrode area of the pixel light source. The etching stepfurther includes a step of etching the exposed micro-lens material layerwith the mask protection. In some embodiments, the exposed micro-lensmaterial layer is etched by a wet etching method. In some embodiments,the opening for an electrode is positioned outside the display arrayarea.

As described above, FIGS. 6A to 6D show various fabrication methods toform a display panel integrated with a micro-lens array. It should beunderstood that these are merely examples, and other fabricationtechniques can also be used.

Although the detailed description contains many specifics, these shouldnot be construed as limiting the scope of the invention but merely asillustrating different examples and aspects of the invention. It shouldbe appreciated that the scope of the invention includes otherembodiments not discussed in detail above. For example, micro-lenseswith different shape bases may also be used, such as square base orother polygon base.

FIG. 7 is a cross-sectional view 700 of three single pixel tri-color LEDdevices 710, 720 and 730 along the diagonal line such as 102 in FIG. 1Aon a substrate 104, in accordance with some embodiments. In someembodiments, although not all shown in FIG. 7, each of the single pixeltri-color LED devices 710, 720 and 730 has similar structures as any oneof the single pixel tri-color LED devices shown in FIGS. 1-6. Thecross-sectional view for a single pixel tri-color LED device 710 withinthe rectangle 750 is equivalent to the cross sectional views as shown inany of the FIGS. 1-6 as described above.

In some embodiments, as shown in any of the embodiments in FIGS. 1-7,the single pixel tri-color LED device further comprises one or morereflective cup structures, such as 702, 704 and 706. The reflectivestructures, such as 702, 704 and 706 surrounds each of the single pixeltri-color LED devices 710, 720 and 730. The reflective cup may be formedon the semiconductor substrate 104 and positioned around the lightemitting region where light from the single pixel tri-color LED deviceis emitted. For example, as shown in FIGS. 1A-1C, from thecross-sectional view along the 102 direction in FIG. 1B, and from thecross-sectional view along the 150 direction in FIG. 1C, the reflectivecup may include four reflective cup parts 146, 148, 170 and 172. In someembodiments, the reflective cup parts 146, 148, 170 and 172 may beformed on the semiconductor substrate 104 and positioned around thelight emitting region. In some embodiments, the reflective cup canisolate at least some of the light or substantially all the lightemitted from the light emitting region. For example, as shown in FIGS.1B-1C, when a height of the reflective cup is higher than a height ofthe light emitting region, the reflective cup parts 146, 148, 170 and172 can isolate the at least some of the light or substantially all thelight emitted from the light emitting region. Therefore, the reflectivecup can suppress the inter-pixel light crosstalk and improve the overallcontrast of LED displays. The reflection from the reflective cup alsoincreases the light emitting efficiency and brightness by focusing thelight emission into a certain direction.

In some embodiments, the height of the reflective cup may be larger thana height of the bottom LED structure, such as the red LED structure,larger than a height of the middle LED structure, such as the green LEDstructure, or larger than a height of the top LED structure, such as theblue LED structure. In some embodiments, the total height of thereflective cup may be larger than a height of the combined height of thebottom LED structure, such as the red LED structure, the middle LEDstructure, such as the green LED structure, and the top LED structure,such as the blue LED structure. In some embodiments, the total height ofthe reflective cup may be larger than the height of the single pixeltri-color LED device without the planarized layer. In some embodiments,the height of the reflective cup is between 0.5 micron to 50 microns. Insome embodiments, the height of the reflective cup is between 1 micronto 20 microns. In some embodiments, the height of the reflective cup isbetween 2 microns to 10 microns. In a preferred embodiment, the heightof the reflective cup is about 2.5 microns while the height of thesingle pixel tri-color LED device without the planarized layer is about1.9 microns. Yet in some embodiments, the reflective cup parts 146, 148,170 and 172 may have different heights. In some embodiments, thecross-section of a reflective cup part such as 146 or 148 is a triangle.In some embodiments, the cross-section of a reflective cup part such as146 or 148 is a trapezoid with bottom edge longer than top edge. In someembodiments, the bottom width of the reflective cup part such as 146 or148 is between 0.3 micron to 50 microns. In some embodiments, the bottomwidth of the reflective cup part such as 146 or 148 is between 0.5micron to 25 microns. In a preferred embodiment, the bottom width of thereflective cup part such as 146 or 148 is about 1 micron. In someembodiments, the distance of the nearest edge of the bottom of thereflective cup part such as 146 or 148 to the nearest edge of bottom ofthe single pixel tri-color LED device, is between 0.2 micron to 30microns. In some embodiments, the distance of the nearest edge of thebottom of the reflective cup part such as 146 or 148 to the nearest edgeof bottom of the single pixel tri-color LED device, is between 0.4micron to 10 microns. In a preferred embodiment, the distance of thenearest edge of the bottom of the reflective cup part such as 146/446 or148/448 to the nearest edge of bottom of the single pixel tri-color LEDdevice, such as the p-electrode connection structure 422 as shown inFIG. 4B, is about 0.6 micron.

In some embodiments, the distance between the centers of the adjacentreflective cup part such as 146/446 and 148/448 of the single pixeltri-color LED device, is between 1 micron to 50 microns. In a preferredembodiment, the distance between the centers of the adjacent reflectivecup part such as 146 and 148 of the single pixel tri-color LED device,is about 5 microns.

In some embodiments, a divergence angle of 0° may correspond to lightpropagating perpendicular to a top surface of the light emitting region,and a divergence angle of 90° may correspond to light propagatingparallel to the top surface of the light emitting region. Changing thegeometry of the reflective cup can control the divergence angle of thelight emitting from the light emitting region. Therefore, the reflectivecup may reduce the divergence of the light emitted from the lightemitting region, and enhance the brightness of the single pixelmulti-color LED device. In some embodiments, sidewalls of the reflectivecups 146-1, 148-1, 170-1 and 172-1 as shown in FIGS. 1B-1C may bestraight, curved, wavy, multiline or the combination thereof. In someembodiments, steepness of the sidewalls of the reflective cup parts 146,148, 170 and 172 may be designed to decrease the divergence of the lightemitted from the light emitting region. For example, the angle of thesidewalls of the reflective cup parts 146, 148, 170 and 172 relative toa vertical axis perpendicular to the substrate 104 may be from at least15 degrees to at most 75 degrees. The angle of the sidewalls of thereflective cup parts 146, 148, 170 and 172 relative to a vertical axisperpendicular to the substrate 104 may be from at least 5 degrees to atmost 60 degrees. In some preferred embodiments, the angle of thesidewalls of the reflective cup parts 146, 148, 170 and 172 relative toa vertical axis perpendicular to the substrate 104 may be from at least10 degrees to at most 50 degrees. The reflective cup can also reflectsome of the light emitted from the light emitting region upwardly. Forexample, some of the light emitted from the light emitting region mayarrive at and be reflected upward by the reflective cup parts 146, 148,170 and 172.

In some embodiments, the reflective cup may comprise metal. In someembodiments, the reflective cup may comprise dielectric material such assilicon oxide. In some embodiments, the reflective cup may comprisephotosensitive dielectric material. In some embodiments, thephotosensitive dielectric material may comprise SU-8, photosensitivepolyimide (PSPI), or BCB. In other embodiments, the reflective cup maycomprise photoresist.

In some embodiments, the reflective cup can be fabricated by acombination of deposition, photo-lithography and etching processes. Insome embodiments, the reflective cup may be fabricated by other suitablemethods. In one approach, PSPI is formed into the reflective cup shapeby a photolithography process. Then, a metal layer with a highreflectivity that includes one or more metals such as Pt, Rh, Al, Au,and Ag, a stacked DBR layer including TiO2/SiO2 layers, or any otherlayer with a total reflection property including a multi-layeredOmni-Directional Reflector (ODR), or a combination thereof, is depositedon the whole surface of the multi-color LED device including thereflective cup as a reflective layer by vapor deposition. Next, thereflective layer is shaded by a photoresist in the reflective cup areawhile the reflective layer on the other region is etched, whereby thelight emitting region is exposed.

In a another approach, an isolation layer including one or more of SiO2,Silicon Nitride, or SU8, which is thicker than the stacked LEDstructures, is deposited or spinned on the stacked LED structures. Then,using a photoresist as a mask, the isolation layer is etched and formedinto a reflective cup shape. Next, a metal layer with a highreflectivity that includes one or more metals such as Pt, Rh, Al, Au,and Ag, a stacked DBR layer including TiO2/SiO2 layers, or any otherlayer with a total reflection property including a multi-layeredOmni-Directional Reflector (ODR), or a combination thereof, is depositedon the whole surface of the multi-color LED device including thereflective cup as a reflective layer by vapor deposition. Finally, thereflective layer is shaded by a photoresist in the reflective cup areawhile the reflective layer on the other region is etched, whereby thelight emitting region is exposed.

In some embodiments, as shown in FIGS. 2-6, the single pixel tri-colorLED device further comprises one or more top electrodes (e.g., topelectrodes 140/440, 442 and 444) integrated with the reflective cup. Theone or more top electrodes may electrically connect with the topelectrode (layer) 140/440. For example, as shown in FIG. 4B, theelectrodes 442 and 444 can be integrated with the reflective cup, e.g.,the reflective cup parts 446 and 448, respectively. Both of the topelectrodes 442 and 444 may extend towards the light emitting region andelectrically connect with the top electrode (layer) 140/440. Thereflective cup may perform as a common P-electrode or N-electrode forthe single pixel tri-color LED device with the adoption of the one ormore top electrodes. For example, when the top electrode (layer) 140/440electrically connect with each of the LED structures (e.g. the LEDstructures including the light emitting layers 112/412, 130/430 and136/436) and optionally the top electrodes 442 and 444, the reflectivecup may perform as a common P-electrode or N-electrode of the singlepixel tri-color LED device.

In some embodiments, the reflective cup further includes one or morereflective coatings. The one or more reflective coatings may be disposedon one or more sidewalls of the reflective cup, e.g., the sidewalls ofthe reflective cup 146-1, 148-1, 170-1 and 172-1. A bottom of each ofthe one or more reflective coatings does not contact the each of the LEDstructures, e.g. the red, green and blue LED structures. The one or morereflective coatings can reflect light emitted from the light emittingregion and therefore enhance the brightness and luminous efficacy ofmicro-LED panels or displays. For example, the light emitted from thelight emitting region may arrive at the one or more reflective coatingsand may be reflected upward by the one or more reflective coatings.

The one or more reflective coatings, together with the reflective cup,can utilize reflection direction and/or reflection intensity of thelight emitted from the light emitting region. For instance, thesidewalls of the reflective cup 146-1, 148-1, 170-1 and 172-1 beinclined at a certain angle, and therefore the one or more reflectivecoatings disposed on the sidewalls of the reflective cup 146-1, 148-1,170-1 and 172-1 are inclined at the same angle as the sidewalls of thereflective cup 146-1, 148-1, 170-1 and 172-1. When the light emittedfrom the light emitting region arrives at the one or more reflectivecoatings, the light emitted from the light emitting region would bereflected by the one or more reflective coatings in accordance with theangle of the sidewalls of the reflective cup 146-1, 148-1, 170-1 and172-1.

Materials of the one or more reflective coatings may be highlyreflective with a reflectivity greater than 60%, 70% or 80%, andtherefore most of the light emitted from the light emitting region canbe reflected. In some embodiments, the one or more reflective coatingsmay comprise one or more metallic conductive materials with highreflectivity. In these embodiments, the one or more metallic conductivematerials may comprise one or more of aluminum, gold or silver. In othersome embodiments, the one or more reflective coatings can bemulti-layered. To be more specific, the one or more reflective coatingsmay comprise a stack of one or more reflective material layers and oneor more dielectric material layers. For example, the one or morereflective coatings may comprise one reflective material layer and onedielectric material layer. In other embodiments, the one or morereflective coatings may comprise two reflective material layers and onedielectric material layer positioned between the two reflective materiallayers. Yet in some other embodiments, the one or more reflectivecoatings may comprise two dielectric material layers and one reflectivematerial layer positioned between the two dielectric material layers. Insome embodiments, the multi-layered structure may comprise two or moremetal layers, which may comprise one or more of TiAu, CrAl or TiWAg.

In some embodiments, the one or more reflective coatings may bemulti-layered Omni-Directional Reflector (ODR), which comprises a metallayer and a Transparent and Conductive Oxides (TCO) layer. For example,the multilayered structure may comprise a dielectric material layer, ametal layer and a TCO layer. In some embodiments, the one or morereflective coatings may comprise two or more dielectric material layers,which are disposed alternately to form a Distributed Bragg Reflector(DBR). For example, the one or more reflective coatings may comprise adielectric material layer, a metal layer and a transparent dielectriclayer. The transparent dielectric layer may comprise one or more ofSiO₂, Si₃N₄, Al₂O₃, or TiO₂. The one or more reflective coatings mayfurther comprise a dielectric material layer, a TCO and a DBR. In otherembodiments, the one or more reflective coatings may comprise one ormore metallic conductive materials with high reflection. In theseembodiments, the one or more metallic conductive materials may compriseone or more of aluminum, gold or silver. In some embodiments, thereflective coatings may have the same the composition, structure andfabrication process as the reflective layers, such as 109, 115, 127,133, and 135 above and below the light emitting layers as describedabove.

In some embodiments, the one or more reflective coatings can beconductive, and then the one or more reflective coatings may alsoperform function as electrical contacts to the single pixel multi-colorLED device. For example, the top electrode (layer) 140 may beelectrically connected with the one or more reflective coatings. Foranother example, one or more reflective coatings may be electricallyconnect with the one or more transparent electrode contact layers 114,132 and 138. The one or more reflective coatings may be patterned to notblock light emitted from the light emitting region. The one or morereflective coatings may then also function as the common electrode forthe LED structures within a single pixel multi-color LED device and/orthe LEDs on a display panel.

In some embodiments, a top conductive layer for connecting to theelectrodes is formed on the top of multi-color LED device, and the topconductive layer is electrically connected with the reflective cup. Insome embodiments, the top conductive layer directly contacts with a topof the reflective cup or a bottom of the reflective cup.

In some embodiments, a bottom dielectric layer is formed between abottom of the reflective cup and the semiconductor substrate.

In some embodiments, the one or more of reflective coatings can beproduced by one or more of electron beam deposition or sputteringprocess.

In some embodiments, the reflective cup can have the shape of a stairlike structure. FIG. 8 is a cross-sectional view of a single pixeltri-color LED device 800 with a stair-shaped reflective cup, along thediagonal line such as 402 in FIG. 4A, in accordance with someembodiments. In some embodiments, although not all shown in FIG. 8, thesingle pixel tri-color LED device 800 has similar structures as any oneof the single pixel tri-color LED devices shown in FIGS. 1-7 with thereflective cup parts, such as 146, 148, 170 and 172, having astair-shaped reflective cup. The stair-shaped reflective cup may beformed on the semiconductor substrate 104/404 and positioned around thelight emitting region. For example, as shown in FIG. 8, from thecross-sectional view along the diagonal line such as 402 in FIG. 4A, thestair-shaped reflective cup may include two stair-shaped reflective cupparts 846 and 848. The stair-shaped reflective cup parts 846 and 848 maybe formed on the semiconductor substrate 104/404, and positioned aroundthe light emitting region. In some embodiments, the stair-shapedreflective cup can isolate at least some or substantially all of thelight emitted from the light emitting region. For example, as shown inFIG. 8, when a height of the stair-shaped reflective cup is higher thana height of the light emitting region, the stair-shaped reflective cupparts 846 and 848 can isolate the at least some or substantially all ofthe light emitted from the light emitting region. Therefore, thestair-shaped reflective cup can suppress the inter-pixel light crosstalkand improve the overall contrast of LED displays.

In some embodiments, the stair-shaped reflective cup includes one ormore stair structures such as 846-1, 846-2, 846-3, 848-1, 848-2, and848-3. In some embodiments, the height each of the stair of thereflective cup may be the same as a height of the LED structure in thesame vertical level. For example, the stair structures 846-1 and 848-1each have the same height as the bottom LED structure. The stairstructures 846-2 and 848-2 each have the same height as the middle LEDstructure. The stair structures 846-3 and 848-3 each have the sameheight as the top LED structure. Yet in some embodiments, thestair-shaped reflective cup parts 846 and 848 may have the same ordifferent heights. The stair-shaped reflective cup can also reflect someof the light emitted from the light emitting region upwardly. Forexample, some of the light emitted from the light emitting region mayarrive at and be reflected by the stair-shaped reflective cup parts 846and 848 upwardly for each LED structures within the single pixelmulti-color LED device in a different pattern according to the design.For example, each of the stair can adjust the focus for the lightemitted (especially horizontally) in a different pattern. For example,focusing the red light more at the center and the blue light more at theedge of the light beam from the LED device. Therefore, it may reduce thedivergence of the light emitted from the light emitting region, andenhance the brightness of the single pixel multi-color LED device.

In some embodiments, the stair-shaped reflective cup structure mayinclude or form a cavity surrounding the light emitting region. Thecavity may include the area surrounded by the stair-shaped reflectivecup and above the semiconductor substrate 404. The cavity may include aninner sidewall, and the inner sidewall may include a plurality ofinclined surfaces. For example, as shown in FIG. 8, the stair-shapedreflective cup may include or surround the cavity, which may include thearea between the stair-shaped reflective parts 846 and 848 and above thesemiconductor substrate 404. The light emitting region may be positionedin the cavity, and surrounded by the stair-shaped reflective cup parts846 and 848.

In some embodiments, a top of the cavity is higher than a top of thelight emitting region. For example, the top of the cavity included inthe stair-shaped reflective cup (e.g., the stair-shaped reflective cupparts 846 and 848) is higher than the top of the light emitting region.In some embodiments, the cavity may include an inner sidewall, and theinner sidewall may include a plurality of inclined surfaces (e.g.,inclined surfaces 846-1S, 846-2S, 846-3S, 848-1S, 848-2S, and 848-3S).In some embodiments, inclined angles (relative to the surface of thesubstrate 404) of the plurality of inclined surfaces from bottom to topof the cavity become greater. For example, as shown in FIG. 8, theangles of the inclined surfaces 846-1S, 846-2S, 846-3S are indicated asinclined angles α, β and γ, respectively. Inclined angles of theinclined surfaces 846-1S, 846-2S, and 846-3S may be the same as theinclined angles of inclined surfaces 848-1S, 848-2S, and 848-3S,respectively. In some embodiments, the inclined angles α, β and γ staythe same or become greater from bottom to top of the cavity. In somepreferred embodiments, the inclined angles α, β and γ may become smallerfrom bottom to top of the cavity, therefore the light emitted from theLED device may be more divergent toward the upper portion of the LEDdevice. Yet in some embodiments, the inclined angles α, β and γ may beany angle according to the design. In some embodiments, the cavity maybe filled with materials containing silicon, e.g., silicon oxide, andthe filling can improve optical refraction, increase transparency,and/or enhance ultraviolet aging resistance and thermal agingresistance. In some embodiments, the cavity may be empty or vacuumed. Insome embodiments, the inclined surfaces (e.g., inclined surfaces 846-1S,846-2S, 846-3S, 848-1S, 848-2S, and 848-3S) may be straight, curved,wavy, multiline or the combination thereof.

In some embodiments, the cavity may include a plurality of sub-cavities.The sub-cavities may be formed or surrounded by respective inclinedsurfaces and may have different dimensions in the horizontal direction.For example, there can be three sub-cavities as shown in FIG. 8. Thesub-cavity at the bottom of the cavity may include the area surroundedor restrained by the semiconductor substrate 104/404, the inclinedsurfaces 846-1S and 848-1S, and bottom of the bonding layer 156/456. Thesub-cavity in middle of the cavity may include the area surrounded orrestrained by the bottom of the bonding layer 156/456, the inclinedsurfaces 846-2S and 848-2S, and bottom of the bonding layer 160/460. Thesub-cavity on top of the cavity may include the area surrounded orrestrained by the bottom of the bonding layer 160/460, the inclinedsurfaces 846-3S and 848-3S, and the top electrode layer 140/440 (or theopening top of the top of the stair structures 846-3 and 848-3). In someembodiments, inclined surfaces of the sub-cavities are not arranged in asame plane. For example, as shown in FIG. 8, the sub-cavities may beformed or surrounded by the plurality of inclined surfaces 846-1S,846-2S, 846-3S, 848-1S, 848-2S, and 848-3S and may have differentdimensions in the horizontal direction. In some embodiments, theinclined surfaces 846-1S, 846-2S, and 846-3S may not be arranged in thesame plane, and the inclined surfaces 848-1S, 848-2S, and 848-3S may notbe arranged in a same plane. For example, the inclined surfaces 846-1S,846-2S, and 846-3S are stagger arranged in different planes in verticaldirection.

In some embodiments, heights of the sub-cavities may be different. Forexample, a height of the sub-cavity in the middle of the cavity may beless than heights of other sub-cavities. A height of the sub-cavity atthe top of the cavity may be larger than a height of the sub-cavity atthe bottom of the cavity. Yet in some embodiments, each of the color LEDstructures is in a respectively different one of the sub-cavities. Forexample, the bottom red LED structure is in the sub-cavity at the bottomof the cavity and the top blue LED structure is in the sub-cavity at thetop of the cavity. The middle green LED structure is in the sub-cavityin the middle of the cavity. In some embodiments, the sub-cavities maybe filled with materials containing silicon, e.g., silicon oxide, andthe filling can improve optical refraction, increase transparency,and/or enhance ultraviolet aging resistance and thermal agingresistance. In some embodiments, materials of the sub-cavities may bedifferent. For example, the material of the sub-cavity at the top of thecavity may be filled with silicon oxide and the material of thesub-cavity at the bottom of the cavity may be filled with epoxy methylsilicon. In some embodiments, the sub-cavities may be empty or vacuumed.

In some embodiments, the stair-shaped reflective cup may comprise metal.In some embodiments, the stair-shaped reflective cup may comprisedielectric material such as silicon dioxide. In some embodiments, thestair-shaped reflective cup may comprise photosensitive dielectricmaterial. In some embodiments, the photosensitive dielectric materialmay comprise SU-8 or photosensitive polyimide (PSPI). In otherembodiments, the stair-shaped reflective cup may comprise photoresist.In some embodiments, the fabrication processes of the stair-shapedreflective cup are similarly described above with reference to thereflective cup.

In some embodiments, the single pixel multi-color LED device 800 furthercomprise one or more reflective coatings. The one or more reflectivecoatings may be disposed on one or more inclined surfaces of thestair-shaped reflective cup, e.g., the inclined surfaces 846-1S, 846-2S,846-3S, 848-1S, 848-2S, and 848-3S. A bottom of each of the one or morereflective coatings does not contact the each of the LED structures,e.g. the red, green and blue LED structures. The one or more reflectivecoatings can reflect light emitted from the light emitting region andtherefore enhance the brightness and luminous efficacy of micro-LEDpanels or displays. For example, the light emitted from the lightemitting region may arrive at the one or more reflective coatings andmay be reflected upwardly by the one or more reflective coatings.

The one or more reflective coatings, together with the stair-shapedreflective cup, can utilize reflection direction and/or reflectionintensity of the light emitted from the light emitting region. Forinstance, the inclined angles α, β and γ of their respectively inclinedsurfaces 846-1S, 846-2S, and 846-3S may become smaller from bottom totop of the cavity, and therefore the one or more reflective coatingsdisposed on the inclined surfaces 846-1S, 846-2S, and 846-3S areinclined at the same angles as the inclined surfaces 846-1S, 846-2S, and846-3S. When the light emitted from the light emitting region arrives atthe one or more reflective coatings, the light emitted from the lightemitting region would be reflected by the one or more reflectivecoatings in accordance with the inclined angles α, β and γ. The inclinedangles α, β and γ may become greater, same or smaller, or the inclinedangles α, β and γ otherwise are chosen according to a specific design.

Materials of the one or more reflective coatings may be highlyreflective with a reflectivity greater than 60%, 70% or 80%, andtherefore most of the light emitted from the light emitting region canbe reflected. In some embodiments, the materials of the one or morereflective coatings are similarly described above with the reference tothe reflective cup. In some embodiments, the materials of one or morereflective coatings disposed on each of inclined surfaces may bedifferent. For example, the material of the reflective coating disposedon the inclined surface 846-1S may be different than the materials ofthe reflective coatings disposed on the inclined surfaces 846-2S, and846-3S respectively.

In some embodiments, the one or more of reflective coatings can beproduced by one or more of electron beam deposition or sputteringprocess. In some embodiments, each of the one or more stair structuressuch as 846-1, 846-2, 846-3, 848-1, 848-2, and 848-3 are formed layer bylayer in a multi-step process. For example, the stair structures such as846-1 and 848-1 are formed in the same step either before or after theplanarized layer 454 is formed. The stair structures such as 846-2 and848-2 are formed in the same step either before or after the planarizedlayer 458 is formed. The stair structures such as 846-3 and 848-3 areformed in the same step either before or after the planarized layer 462is formed. In some embodiments, especially when layer by layerplanarization is involved in the process for forming the single pixeltri-color LED device, the stair structures are formed as a result of thelayer by layer process and the dislocation of the bonding of thedifferent planarized layers including the LED structures. In someembodiments, there may be gaps (not shown in FIG. 8) between thedifferent stair structures such as 846-1, 846-2, and 846-3 as a resultof the layer by layer process and the dislocation of the bonding of thedifferent planarized layers including the LED structures.

In some embodiments, the reflective cup can have a floating structure.FIG. 9 is a cross-sectional view of a single pixel tri-color LED device900 with a floating reflective cup, along the diagonal line such as 402in FIG. 4A, in accordance with some embodiments. In some embodiments,although not all shown in FIG. 9, the single pixel tri-color LED device900 has similar structures as any one of the single pixel tri-color LEDdevices shown in FIGS. 1-8 with the floating reflective cup parts, suchas 946 and 948.

In some embodiments, the floating reflective cup may surround the lightemitting region and the bottom of the reflective cup does not directlycontact the semiconductor substrate 104/404. For example, as shown inFIG. 9, the reflective cup parts 946 and 948 surround the light emittingregion, and bottoms of the reflective cup parts 946 and 948 do notdirectly contact the semiconductor substrate 104, e.g., there is a gapbetween the bottom of the reflective cup and the substrate 104/404. Insome embodiments, the gap is filled by the planarized insulation layer454. In some embodiments, the light emitted from the light emittingregion may arrive at and be reflected upward by the reflective cup. Forexample, as shown in FIG. 9, the light emitted from the light emittingregion, including light emitting from sidewalls and/or tops of the LEDstructures, may arrive at the reflective cup parts 946 and 948, and bereflected upward by the reflective cup parts 946 and 948. Therefore, itmay reduce the divergence of the light emitted from the light emittingregion, and enhance the brightness of the single pixel multi-color LEDdevice.

In some embodiments, the distance between the bottom of the reflectivecup and the top surface of the semiconductor substrate 104/404 can beadjusted according to the design needs. In some embodiments, thedistance between the bottom of the reflective cup and the top surface ofthe semiconductor substrate 104/404 may be adjusted during manufacturingprocess of the single pixel multi-color LED device and the displaypanel. When manufacture of the single pixel multi-color LED device 900is completed, the distance is fixed and not adjustable. In otherembodiments, the distance between the bottom of the reflective cup andthe top surface of the semiconductor substrate 104/404 may bespecifically selected during the design process, and will be fixed aftermanufacturing the single pixel multi-color LED device 900 and thedisplay panel. In some embodiments, the distance between the bottom ofthe reflective cup, such as the parts 946 and 948, to the top surface ofthe substrate 404 the may be the same or smaller than the distancebetween the top surface of the bonding layer 408 at the bottom of thelight emitting layer 412 to the top surface of the substrate 404. Insome embodiments, the distance between the bottom of the reflective cup,such as the parts 946 and 948, to the top surface of the substrate 404the may be larger than the distance between the top surface of thebonding layer 408 at the bottom of the light emitting layer 412 to thetop surface of the substrate 404. By adjusting the gap of the floatingreflective cup, certain light from a particular portion of the singlepixel multi-color LED device 900 may not be reflected or isolated, thatcould make the light more focused at selected portions of the device900.

In some embodiments, the distance between the bottom of the reflectivecup and the top surface of the semiconductor substrate 404 can be lessthan 0.5 micrometer. In some embodiments, the distance between thebottom of the reflective cup and the top surface of the semiconductorsubstrate 404 can be less than 1 micrometer. In some embodiments, thedistance between the bottom of the reflective cup and the top surface ofthe semiconductor substrate 140 can be less than 2 micrometers. In someembodiments, the distance between the bottom of the reflective cup andthe top surface of the semiconductor substrate 404 can be less than 5micrometers. In some embodiments, the distance between the bottom of thereflective cup and the top surface of the semiconductor substrate 404can be less than 10 micrometers. In some embodiments, the distancebetween the bottom of the reflective cup and the top surface of thesemiconductor substrate 404 can be less than 20 micrometers. In someembodiments, the distance between the bottom of the reflective cup andthe top surface of the semiconductor substrate 404 can be less than 50micrometers. In some embodiments, the distance between the bottom of thereflective cup and the top surface of the semiconductor substrate 404can be less than 75 micrometers. In some embodiments, the distancebetween the bottom of the reflective cup and the top surface of thesemiconductor substrate 404 can be less than 100 micrometers. Generally,the distance between bottom of the reflective cup and top surface of thesemiconductor substrate 404 is decided by the height of the bottom ofthe light emitting layer, such as the thickness of metal bonding layer.In a preferred embodiment, the distance between bottom of the reflectivecup and top surface of the semiconductor substrate 404 is not more than20 micrometers.

In some embodiments, the reflective cup can isolate at least some of thelight emitted from the light emitting region. For example, as shown inFIG. 9, when a height of the reflective cup is higher than a height ofthe light emitting region, the reflective cup parts 946 and 948 canisolate the at least some of the light emitted from the light emittingregion. Therefore, the reflective cup can suppress the inter-pixel lightcrosstalk and improve the overall contrast of LED displays. The floatingreflective cup has the same or similar composition, shape andfabrication process (except the position and location) as the reflectivecups as described above.

FIGS. 1-9 only illustrate the single pixel multi-color LED devicesaccording to some embodiments. In other embodiments, the reflective cupcan be different shapes when seen from a top view or side view. That is,the sidewalls of the reflective cup surrounding the light emittingregion may be circle, triangle, square, rectangular, pentagonal,hexagonal and octagonal. The sidewalls of the reflective cup maysurround one light emitting region or one single pixel multi-color LEDdevice, or a group of light emitting regions or a group of single pixelmulti-color LED devices. For example, the sidewalls of the reflectivecup may surround two or more light emitting regions or single pixelmulti-color LED devices which are arranged in the same plane.

An array of the single pixel multi-color LED devices, each of which maycomprise a reflective cup, can be utilized. Each of the reflective cupcan have different shapes, when seen from a top view or plan view. Forexample, a reflective cup of a first single pixel multi-color LED devicemay be circle, and a reflective cup of an adjacent single pixelmulti-color LED device may be square. In addition, the reflective cupscan be electrically isolated from each other. The reflective cups canalso be isolated if buffer space is provided between adjacent reflectivecups or if the material of the reflective cups may not extend all theway to the boundary with the adjacent reflective cup. Alternately, areflective coating form on the sidewall of the reflective cup can simplybe extended to cover the interstitial areas between adjacent reflectivecups. In another embodiment, the reflective cups can be electricallyconnected with each other by a common electrode such as a top electrode.

Various other modifications, changes and variations which will beapparent to those skilled in the art may be made in the arrangement,operation and details of the method and apparatus of the presentinvention disclosed herein without departing from the spirit and scopeof the invention as defined in the appended claims. Therefore, the scopeof the invention should be determined by the appended claims and theirlegal equivalents.

Further embodiments also include various subsets of the aboveembodiments including embodiments shown in FIGS. 1-9 combined orotherwise re-arranged in various other embodiments.

Various design aspects of the single pixel multi-color LED device, suchas the dimensions of the layers (e.g., width, length, height, andcross-sectional area of each layer), the dimension of the electrodes,size, shape, spacing, and arrangement of the two or more LED structurelayers, bonding layers, reflective layers and the conductive layers, andthe configuration between the integrated circuits, pixel driver andelectrical connections are selected (e.g., optimized using a cost orperformance function) for obtaining the desired LED characteristics. LEDcharacteristics that vary based on the above design aspects include,e.g., size, materials, cost, fabrication efficiency, light emissionefficiency, power consumption, directivity, luminous intensity, luminousflux, color, spectrum and spatial radiation pattern.

FIG. 10A is a circuit diagram illustrating a matrix of single pixeltri-color LED devices 1000, in accordance with some embodiments. Thecircuit in FIG. 10A includes three pixel drivers 1002, 1004, and 1006and three tri-color LED devices 1008, 1010, and 1012.

In some embodiments, a display panel includes a plurality of pixels,such as millions of pixels, and each pixel includes a tri-color LEDdevice structure. In some embodiments, the LED device structures can bemicro LEDs. Micro LEDs typically have a lateral dimension of 50 microns(um) or less, and can have lateral dimensions less than 10 um and evenjust a few um.

In some embodiments, the pixel driver, for example 1002, includes anumber of transistors and capacitors (not shown in FIG. 10A). Thetransistors include a driving transistor connected to a voltage supply,and a control transistor configured with its gate connected to a scansignal bus line. The capacitors include a storage capacitor are used tomaintain the gate voltage of the driving transistor during the time thatthe scan signal is setting other pixels.

In this example, each of the three tri-color LED devices, for example1008, have its own integrated circuit (IC) pixel driver 1002. Thetri-color LED device 1008 for a single pixel can be viewed as threeindividual LEDs with different colors connected in parallel. Forexample, the red LED 1018, green LED 1016, and blue LED 1014, within thesame tri-color LED device 1008, are connected to the same IC pixeldriver 1002 via a shared P-electrode pad or anode.

In some embodiments, each of the red, green, and blue LEDs within thesame tri-color LED device 1008 is connected to separate N-electrode pador cathode.

In some embodiments, all the red LEDs, for example, 1018, 1024 and 1030,from different tri-color LED devices, are connected to the same commonN-electrode 1036. All the green LEDs for example, 1016, 1022 and 1028,from different tri-color LED devices, are connected to the same commonN-electrode 1034. All the blue LEDs, for example, 1014, 1020 and 1026,from different tri-color LED devices, are connected to the same commonN-electrode 1032. The use of the common electrodes simplifies thefabrication process and reduces the area of the LED devices especiallythe footprint of the electrodes.

In some embodiments, the connections for the P-electrode and N-electrodecan be switched and interchanged (not shown in FIG. 10A). For example,the red LED 1018, green LED 1016, and blue LED 1014, within the sametri-color LED device 1008, are connected to a shared N-electrode pad orcathode. Each of the red, green, and blue LEDs within the same tri-colorLED device 1008 is connected to separate P-electrode pad or anode. Allthe red LEDs, for example, 1018, 1024 and 1030, from different tri-colorLED devices, are connected to the same common N-electrode 1036.

FIG. 10B is a circuit diagram illustrating a matrix of single pixeltri-color LED devices 1000, in accordance with some embodiments. FIG.10B is similar as FIG. 10A except that in this example, each of the LEDstructures, in each of the three tri-color LED devices, for example1008, have its own integrated circuit (IC) pixel driver 1002. Forexample, the red LED 1018, green LED 1016, and blue LED 1014, within thesame tri-color LED device 1008, are connected to the different IC pixeldrivers 1002-1, 1002-2, and 1002-3 respectively via a separateP-electrode pad or anode. As can be seen from FIGS. 1-9, this type ofP-electrode connections are illustrated in some embodiments.

In addition, in some embodiments as shown in FIG. 10B, all the LEDs ofdifferent colors, from different tri-color LED devices, are connected tothe same common N-electrode 1032.

In some embodiments, the connections for the P-electrode and N-electrodecan be switched and interchanged (not shown in FIG. 10B). For example,the red LED 1018, green LED 1016, and blue LED 1014, within the sametri-color LED device 1008, are connected to the different N-electrodepad or cathode respectively. All the LEDs of different colors, fromdifferent tri-color LED devices, are connected to the same commonP-electrode 1032.

FIG. 11 is a top view of a micro LED display panel 1100, in accordancewith some embodiments. The display panel 1100 includes a data interface1110, a control module 1120 and a pixel region 1150. The data interface1110 receives data defining the image to be displayed. The source(s) andformat of this data will vary depending on the application. The controlmodule 1120 receives the incoming data and converts it to a formsuitable to drive the pixels in the display panel. The control module1120 may include digital logic and/or state machines to convert from thereceived format to one appropriate for the pixel region 1150, shiftregisters or other types of buffers and memory to store and transfer thedata, digital-to-analog converters and level shifters, and scancontrollers including clocking circuitry.

The pixel region 1150 includes an array of pixels. The pixels includemicro LEDs, such as a multi-color LED 1134, integrated with pixeldrivers, for example as described above. In some embodiments, an arrayof micro-lens (not separately shown from the LED 1134 in FIG. 11) coversthe top of the array of the multi-color LEDs. In some embodiments, anarray of optical isolation structures, such as reflective structures orreflective cups (not separately shown from the LED 1134 in FIG. 11) areformed around the array of the multi-color LEDs. In this example, thedisplay panel 1100 is a color RGB display panel. It includes red, greenand blue pixels. Within each pixel, the tri-color LED 1134 is controlledby a pixel driver. The pixel makes contact to a supply voltage (notshown) and ground via a ground pad 1136, and also to a control signal,according to the embodiments shown previously. Although not shown inFIG. 11, the p-electrode of the tri-color LED 1134 and the output of thedriving transistor are positioned within the LED 1134. The LED currentdriving signal connection (between p-electrode of LED and output of thepixel driver), ground connection (between n-electrode and systemground), the supply voltage Vdd connection (between source of the pixeldriver and system Vdd), and the control signal connection to the gate ofthe pixel driver are made in accordance with various embodiments.

FIG. 11 is merely a representative figure. Other designs will beapparent. For example, the colors do not have to be red, green and blue.They also do not have to be arranged in columns or stripes. As oneexample, apart from the arrangement of a square matrix of pixels shownin FIG. 11, an arrangement of hexagonal matrix of pixels can also beused to form the display panel 1100.

In some applications, a fully programmable rectangular array of pixelsis not necessary. Other designs of display panels with a variety ofshapes and displays may also be formed using the device structuresdescribed herein. One class of examples is specialty applications,including signage and automotive. For example, multiple pixels may bearranged in the shape of a star or a spiral to form a display panel, anddifferent patterns on the display panel can be produced by turning onand off the LEDs. Another specialty example is automobile headlights andsmart lighting, where certain pixels are grouped together to formvarious illumination shapes and each group of LED pixels can be turnedon or off or otherwise adjusted by individual pixel drivers.

Even the lateral arrangement of devices within each pixel can vary. InFIGS. 1-9, the LEDs and pixel drivers are arranged vertically, i.e.,each LED is located on top of the corresponding pixel driver circuit.Other arrangements are possible. For example, the pixel drivers couldalso be located “behind”, “in front of”, or “beside” the LED.

Different types of display panels can be fabricated. For example, theresolution of a display panel can range typically from 8×8 to 3840×2160.Common display resolutions include QVGA with 320×240 resolution and anaspect ratio of 4:3, XGA with 1024×768 resolution and an aspect ratio of4:3, D with 1280×720 resolution and an aspect ratio of 16:9, FHD with1920×1080 resolution and an aspect ratio of 16:9, UHD with 3840×2160resolution and an aspect ratio of 16:9, and 4K with 4096×2160resolution. There can also be a wide variety of pixel sizes, rangingfrom sub-micron and below to 10 mm and above. The size of the overalldisplay region can also vary widely, ranging from diagonals as small astens of microns or less up to hundreds of inches or more.

Different applications will also have different requirements for opticalbrightness and viewing angle. Example applications include directviewing display screens, light engines for home/office projectors andportable electronics such as smart phones, laptops, wearableelectronics, AR and VR glasses, and retinal projections. The powerconsumption can vary from as low as a few milliwatts for retinalprojectors to as high as kilowatts for large screen outdoor displays,projectors, and smart automobile headlights. In terms of frame rate, dueto the fast response (nanoseconds) of inorganic LEDs, the frame rate canbe as high as KHz, or even MHz for small resolutions.

Further embodiments also include various subsets of the aboveembodiments including the embodiments in FIGS. 1-11 combined orotherwise re-arranged in various embodiments, for example, a multi-colorLED pixel device/unit with and without reflective layers, with andwithout planarized layers, with and without reflective cup structuresincluding various shapes and types of positioning, with and withoutrefractive layers, with and without micro-lenses, with and withoutspacers, and with different electrode connection structures.

Although the detailed description contains many specifics, these shouldnot be construed as limiting the scope of the invention but merely asillustrating different examples and aspects of the invention. It shouldbe appreciated that the scope of the invention includes otherembodiments not discussed in detail above. For example, the approachesdescribed above can be applied to the integration of functional devicesother than LEDs and OLEDs with control circuitry other than pixeldrivers. Examples of non-LED devices include vertical cavity surfaceemitting lasers (VCSEL), photodetectors, micro-electro-mechanical system(MEMS), silicon photonic devices, power electronic devices, anddistributed feedback lasers (DFB). Examples of other control circuitryinclude current drivers, voltage drivers, trans-impedance amplifiers,and logic circuits.

The preceding description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the embodimentsdescribed herein and variations thereof. Various modifications to theseembodiments will be readily apparent to those skilled in the art, andthe generic principles defined herein may be applied to otherembodiments without departing from the spirit or scope of the subjectmatter disclosed herein. Thus, the present disclosure is not intended tobe limited to the embodiments shown herein but is to be accorded thewidest scope consistent with the following claims and the principles andnovel features disclosed herein.

Features of the present invention can be implemented in, using, or withthe assistance of a computer program product, such as a storage medium(media) or computer readable storage medium (media) having instructionsstored thereon/in which can be used to program a processing system toperform any of the features presented herein. The storage medium caninclude, but is not limited to, high-speed random access memory, such asDRAM, SRAM, DDR RAM or other random access solid state memory devices,and may include non-volatile memory, such as one or more magnetic diskstorage devices, optical disk storage devices, flash memory devices, orother non-volatile solid state storage devices. Memory optionallyincludes one or more storage devices remotely located from the CPU(s).Memory or alternatively the non-volatile memory device(s) within thememory, comprises a non-transitory computer readable storage medium.

Stored on any machine readable medium (media), features of the presentinvention can be incorporated in software and/or firmware forcontrolling the hardware of a processing system, and for enabling aprocessing system to interact with other mechanisms utilizing theresults of the present invention. Such software or firmware may include,but is not limited to, application code, device drivers, operatingsystems, and execution environments/containers.

It will be understood that, although the terms “first,” “second,” etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the claims. Asused in the description of the embodiments and the appended claims, thesingular forms “a,” “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willalso be understood that the term “and/or” as used herein refers to andencompasses any and all possible combinations of one or more of theassociated listed items. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

As used herein, the term “if” may be construed to mean “when” or “upon”or “in response to determining” or “in accordance with a determination”or “in response to detecting,” that a stated condition precedent istrue, depending on the context. Similarly, the phrase “if it isdetermined [that a stated condition precedent is true]” or “if [a statedcondition precedent is true]” or “when [a stated condition precedent istrue]” may be construed to mean “upon determining” or “in response todetermining” or “in accordance with a determination” or “upon detecting”or “in response to detecting” that the stated condition precedent istrue, depending on the context.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the claims to the precise forms disclosed. Many modifications andvariations are possible in view of the above teachings. The embodimentswere chosen and described in order to best explain principles ofoperation and practical applications, to thereby enable others skilledin the art to best utilize the invention and the various embodiments.

What is claimed is:
 1. A micro-light emitting diode (LED) pixel unit,comprising, a first color LED structure, formed on an IC substrate,wherein the first color LED structure includes a first light emittinglayer, and a first reflective structure is formed on a bottom of thefirst light emitting layer; a first bonding metal layer, formed at abottom of the first color LED structure, and configured to bond the ICsubstrate and the first color LED structure; a second bonding metallayer, formed on a top of the first color LED structure; a second colorLED structure, formed on the second bonding metal layer, wherein thesecond color LED structure includes a second light emitting layer, and asecond reflective structure is formed on a bottom of the second lightemitting layer; a top electrode layer, covering the first color LEDstructure and the second color LED structure and electrically contactingwith the first color LED structure and the second color LED structure,wherein the IC substrate is electrically connected with the first colorLED structure and the second color LED structure; and a reflective cup,surrounding the first color LED structure and the second color LEDstructure; wherein light emitted from the first light emitting layer andthe second light emitting layer is substantially in a horizontaldirection that arrives at and is reflected upward by the reflective cup.2. The micro-LED pixel unit according to claim 1, wherein the firstreflective structure includes at least one first reflective layer andthe second reflective structure includes at least one second reflectivelayer, reflectivity of the first reflective layer or the secondreflective layer being above 60%.
 3. The micro-LED pixel unit accordingto claim 2, wherein a material of the first reflective layer or thesecond reflective layer comprises one or more of Rh, Al, Ag, or Au. 4.The micro-LED pixel unit according to claim 2, wherein the firstreflective structure includes two first reflective layers and refractiveindices of the two first reflective layers are different, and whereinthe second reflective structure includes two second reflective layersand refractive indices of the two second reflective layers aredifferent.
 5. The micro-LED pixel unit according to claim 4, wherein thetwo first reflective layers comprise SiO₂ and Ti₃O₅ respectively, andthe two second reflectivity layers comprise SiO₂ and Ti₃O₅ respectively.6. The micro-LED pixel unit according to claim 2, wherein the firstreflective structure further includes a first transparent layer on thefirst reflective layer, and the second reflective structure furtherincludes a second transparent layer on the second reflective layer. 7.The micro-LED pixel unit according to claim 6, wherein the firsttransparent layer comprises one or more of indium tin oxide (ITO) orSiO₂, and the second transparent layer comprises one or more of ITO orSiO₂.
 8. The micro-LED pixel unit according to claim 1, wherein thefirst color LED structure further includes a first bottom conductivecontact layer and a first top conductive contact layer, and the secondcolor LED structure further includes a second bottom conductive contactlayer and a second top conductive contact layer; wherein the first lightemitting layer is between the first bottom conductive contact layer andthe first top conductive contact layer, and the second light emittinglayer is between the second bottom conductive contact layer and thesecond top conductive contact layer; wherein the first bottom conductivecontact layer is electrically connected with the IC substrate throughthe first reflective structure and the first bonding metal layer througha first contact via, and the second bottom conductive contact layer iselectrically connected with the IC substrate through a second contactvia; and wherein an edge of the first top conductive contact layer is incontact with the top electrode layer, and a top surface of the secondtop conductive contact layer is in contact with the top electrode layer.9. The micro-LED pixel unit according to claim 1, further comprising athird reflective structure formed on a top of the first light emittinglayer, and a fourth reflective structure formed on a top of the secondlight emitting layer.
 10. The micro-LED pixel unit according to claim 1,further comprising a micro-lens formed above the top electrode layer.11. The micro-LED pixel unit according to claim 10, further comprising aspacer formed between the micro-lens and the top electrode layer. 12.The micro-LED pixel unit according to claim 11, wherein a material ofthe spacer comprises silicon oxide.
 13. The micro-LED pixel unitaccording to claim 10, wherein a lateral dimension of the micro-lens islarger than that of an active emitting area of the first LED structure;and the lateral dimension of the micro-lens is larger than that of anactive emitting area of the second LED structure.
 14. The micro-LEDpixel unit according to claim 1, wherein the first color LED structureand the second color LED structure have a same lateral dimension. 15.The micro-LED pixel unit according to claim 1, wherein the first colorLED structure and the second color LED structure have a same centeraxis.
 16. The micro-LED pixel unit according to claim 2, wherein athickness of the at least one first reflective layer is in a range of 5nm to 10 nm, and a thickness of the at least one second reflective layeris in a range of 5 nm to 10 nm, and wherein a thickness of the firstcolor LED structure is not more than 300 nm, and a thickness of thesecond color LED structure is not more than 300 nm.